Pub Date : 2024-09-30DOI: 10.1016/j.tetlet.2024.155317
Reduction of aldehydes to alcohols is a fundamental organic transformation, typically achieved through metal-catalyzed reductions or by the use of hydride-based reagents. However, these conventional methods often go through harsh conditions with expensive catalysts and additional reductants, limiting their broader applications. In this study, for the first time we introduce an efficient, metal-free reduction strategy using triphenylphosphine (PPh3) and KOtBu in MeOH. This method exhibits broad functional group tolerance, mild environment and selectivity in reducing aldehydes even in the presence of other reactive functionalities (NO2, CN, ketone, etc.). Key features highlight this novel approach with practicality, scalability to gram scales and excellent yields for the reduction of varied aldehydes to alcohols (30 examples; 65–95 % Yields).
{"title":"PPh3-catalyzed chemoselective reduction of aldehydes to alcohols","authors":"","doi":"10.1016/j.tetlet.2024.155317","DOIUrl":"10.1016/j.tetlet.2024.155317","url":null,"abstract":"<div><div>Reduction of aldehydes to alcohols is a fundamental organic transformation, typically achieved through metal-catalyzed reductions or by the use of hydride-based reagents. However, these conventional methods often go through harsh conditions with expensive catalysts and additional reductants, limiting their broader applications. In this study, for the first time we introduce an efficient, metal-free reduction strategy using triphenylphosphine (PPh<sub>3</sub>) and KO<em><sup>t</sup></em>Bu in MeOH. This method exhibits broad functional group tolerance, mild environment and selectivity in reducing aldehydes even in the presence of other reactive functionalities (NO<sub>2</sub>, CN, ketone, etc.). Key features highlight this novel approach with practicality, scalability to gram scales and excellent yields for the reduction of varied aldehydes to alcohols (30 examples; 65–95 % Yields).</div></div>","PeriodicalId":438,"journal":{"name":"Tetrahedron Letters","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142417329","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-30DOI: 10.1016/j.tetlet.2024.155318
Two novel meroterpenoids, arnebic acid A (1) and B (2) with a new 6/10/5 tricyclic system containing a pyran-4-one ring, were isolated from the roots of Arnebia euchroma. Through extensive spectroscopic analysis, single-crystal X-ray crystallography analysis and ECD calculation, the structures with absolute configurations of 1 and 2 were unequivocally elucidated. Additionally, the plausible biosynthetic pathways for compounds 1 and 2 were deduced.
从欧鼠李属植物的根部分离出了两种新的美拉特萜类化合物--欧鼠李酸 A (1) 和 B (2)，它们具有一个包含吡喃-4-酮环的新的 6/10/5 三环系统。通过大量的光谱分析、单晶 X 射线晶体学分析和 ECD 计算，明确地阐明了 1 和 2 的绝对构型结构。此外，还推导出了化合物 1 和 2 的合理生物合成途径。
{"title":"Two novel meroterpenoids with a 6/10/5 tricyclic system containing a pyran-4-one ring from Arnebia euchroma","authors":"","doi":"10.1016/j.tetlet.2024.155318","DOIUrl":"10.1016/j.tetlet.2024.155318","url":null,"abstract":"<div><div>Two novel meroterpenoids, arnebic acid A (<strong>1</strong>) and B (<strong>2</strong>) with a new 6/10/5 tricyclic system containing a pyran-4-one ring, were isolated from the roots of <em>Arnebia euchroma</em>. Through extensive spectroscopic analysis, single-crystal X-ray crystallography analysis and ECD calculation, the structures with absolute configurations of <strong>1</strong> and <strong>2</strong> were unequivocally elucidated. Additionally, the plausible biosynthetic pathways for compounds <strong>1</strong> and <strong>2</strong> were deduced.</div></div>","PeriodicalId":438,"journal":{"name":"Tetrahedron Letters","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142417324","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-29DOI: 10.1016/j.tetlet.2024.155315
Given that the photochromic functional materials possess outstanding phototropic color-change properties, the attention being paid to this field is progressively intensifying. The development of N-heterocyclic carbonyl photoswitching materials, harnessing dithienylethene site for photochromism, typically involves a complex multi-step synthesis process, which substrate diversification and the complexity of the preparation process are confronted with various challenges. Herein, we present a straightforward synthetic methodology for the preparation of photochromic 4,5-bis(2,5-dimethylthiophen-3-yl)-1,3-diphenyl-1,3-dihydro-2H-imidazol-2-one (1o) via reprogramming the synthesis pathway of dithienylethene-containing imidazolone using 1,3-diphenylurea. The current method demonstrates efficient reaction between α-hydroxy ketone and 1,3-diphenylurea in high yield, thereby enabling direct and straightforward one-step cyclization. The grown crystal sample of the targeted 1o has undergone single crystal X-ray diffraction analysis to elucidate its structural information. The ring-open (o-isomer) and ring-closed (c-isomer) forms showing remarkable fatigue resistance and high contrast visual color changes, can be effortlessly interconverted through the alternating irradiation of UV/vis light. To illustrate the electronic structure of the isomers, thorough analyses of the frontier molecular orbital based on TD-DFT calculations were conducted.
{"title":"Highly efficient synthesis and photochromic properties of a pentacyclic N-heterocyclic carbonyl-based dithienylethene","authors":"","doi":"10.1016/j.tetlet.2024.155315","DOIUrl":"10.1016/j.tetlet.2024.155315","url":null,"abstract":"<div><div>Given that the photochromic functional materials possess outstanding phototropic color-change properties, the attention being paid to this field is progressively intensifying. The development of <em>N</em>-heterocyclic carbonyl photoswitching materials, harnessing dithienylethene site for photochromism, typically involves a complex multi-step synthesis process, which substrate diversification and the complexity of the preparation process are confronted with various challenges. Herein, we present a straightforward synthetic methodology for the preparation of photochromic 4,5-bis(2,5-dimethylthiophen-3-yl)-1,3-diphenyl-1,3-dihydro-2<em>H</em>-imidazol-2-one (<strong>1o</strong>) via reprogramming the synthesis pathway of dithienylethene-containing imidazolone using 1,3-diphenylurea. The current method demonstrates efficient reaction between α-hydroxy ketone and 1,3-diphenylurea in high yield, thereby enabling direct and straightforward one-step cyclization. The grown crystal sample of the targeted <strong>1o</strong> has undergone single crystal X-ray diffraction analysis to elucidate its structural information. The ring-open (<em>o</em>-isomer) and ring-closed (<em>c</em>-isomer) forms showing remarkable fatigue resistance and high contrast visual color changes, can be effortlessly interconverted through the alternating irradiation of UV/vis light. To illustrate the electronic structure of the isomers, thorough analyses of the frontier molecular orbital based on TD-DFT calculations were conducted.</div></div>","PeriodicalId":438,"journal":{"name":"Tetrahedron Letters","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142359607","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-29DOI: 10.1016/j.tetlet.2024.155316
A facile synthetic route to isoxazole is reported. Through examination of the reaction of stable nitrile oxides, β-substituted cyclohexenones, particularly sulfinyl and sulfonyl derivatives, show excellent regioselectivity in the 1,3-dipolar cycloaddition, forming isoxazoline cycloadducts, which undergo in-situ 1,2-elimination either with the assistance of a base (for the β-sulfonyl derivative) or without the need for a base (for the β-sulfinyl derivative), enabling a direct, high-yield access to isoxazoles.
{"title":"Facile synthetic route to isoxazoles from β-sulfinyl- and β-sulfonyl-cyclohexenones via regioselective nitrile oxide cycloaddition and in-situ elimination","authors":"","doi":"10.1016/j.tetlet.2024.155316","DOIUrl":"10.1016/j.tetlet.2024.155316","url":null,"abstract":"<div><div>A facile synthetic route to isoxazole is reported. Through examination of the reaction of stable nitrile oxides, β-substituted cyclohexenones, particularly sulfinyl and sulfonyl derivatives, show excellent regioselectivity in the 1,3-dipolar cycloaddition, forming isoxazoline cycloadducts, which undergo in-situ 1,2-elimination either with the assistance of a base (for the β-sulfonyl derivative) or without the need for a base (for the β-sulfinyl derivative), enabling a direct, high-yield access to isoxazoles.</div></div>","PeriodicalId":438,"journal":{"name":"Tetrahedron Letters","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142417325","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-27DOI: 10.1016/j.tetlet.2024.155314
Cyclic peptides are composed of canonical and non-canonical amino acids in a rigid conformation, which endow them high binding affinity and specificity, proteolytic stability, and enhanced membrane permeation compared to linear analogs, thereby making them as promising therapeutics of the future. To date, more than 40 cyclic peptides from nature or derivatives are used as therapeutics, with an average of around one cyclic peptide drug approved per year. This review aims to highlight the past 5 years’ advances in total synthesis of cyclic peptides including monocyclic peptides, bicyclic peptides, and tricyclic peptides, laying a solidly synthetic foundation for drug discovery.
{"title":"Recent progress on total synthesis of cyclic peptides","authors":"","doi":"10.1016/j.tetlet.2024.155314","DOIUrl":"10.1016/j.tetlet.2024.155314","url":null,"abstract":"<div><div>Cyclic peptides are composed of canonical and non-canonical amino acids in a rigid conformation, which endow them high binding affinity and specificity, proteolytic stability, and enhanced membrane permeation compared to linear analogs, thereby making them as promising therapeutics of the future. To date, more than 40 cyclic peptides from nature or derivatives are used as therapeutics, with an average of around one cyclic peptide drug approved per year. This review aims to highlight the past 5 years’ advances in total synthesis of cyclic peptides including monocyclic peptides, bicyclic peptides, and tricyclic peptides, laying a solidly synthetic foundation for drug discovery.</div></div>","PeriodicalId":438,"journal":{"name":"Tetrahedron Letters","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142417323","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-25DOI: 10.1016/j.tetlet.2024.155298
The N-debenzylation of aryl-halogenated amines using the Laccase LAC97/TEMPO system is reported, demonstrating selective N-debenzylation with no dehalogenation of the phenyl ring, which is observed with conventional debenzylation methods such as palladium-catalysed hydrogenation. This reaction was performed under ambient conditions in acidic buffer with 5 % DMSO as co-solvent in an open-to-air vessel. The versatility and robustness of the system was demonstrated on substrates harbouring different halogen moieties. The limitations of the Laccase LAC97/TEMPO system were also studied, highlighting the formation of by-products due to overoxidation on selected substrates. A series of substrates with various halogens were studied. High conversion (78–90 %) in 6 h and full conversion was achieved within 24 h using HPLC to monitor the reaction. Overall, this system is presented as a chemoselective N-debenzylation alternative for aryl-halogenated substrates.
{"title":"Chemoselective oxidative N-debenzylation of aryl halogenated amines using the Laccase LAC97/TEMPO system","authors":"","doi":"10.1016/j.tetlet.2024.155298","DOIUrl":"10.1016/j.tetlet.2024.155298","url":null,"abstract":"<div><div>The N-debenzylation of aryl-halogenated amines using the Laccase LAC97/TEMPO system is reported, demonstrating selective N-debenzylation with no dehalogenation of the phenyl ring, which is observed with conventional debenzylation methods such as palladium-catalysed hydrogenation. This reaction was performed under ambient conditions in acidic buffer with 5 % DMSO as co-solvent in an open-to-air vessel. The versatility and robustness of the system was demonstrated on substrates harbouring different halogen moieties. The limitations of the Laccase LAC97/TEMPO system were also studied, highlighting the formation of by-products due to overoxidation on selected substrates. A series of substrates with various halogens were studied. High conversion (78–90 %) in 6 h and full conversion was achieved within 24 h using HPLC to monitor the reaction. Overall, this system is presented as a chemoselective N-debenzylation alternative for aryl-halogenated substrates.</div></div>","PeriodicalId":438,"journal":{"name":"Tetrahedron Letters","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142320237","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-25DOI: 10.1016/j.tetlet.2024.155311
A quinine-squaramide catalyzed enantioselective inverse-electron-demand hetero-Diels–Alder reaction between γ-butenolides and ortho-hydroxyphenyl p-QMs has been disclosed. A wide range of chiral 3, 4-dihydrocoumarins frameworks with two adjacent stereogenic centers have been directly and concisely prepared in excellent results (up to 94 % yield, 99:1 dr, 98:2 er) under mild conditions.
{"title":"A quinine squaramide catalyzed enantioselective [4 + 2] cycloaddition between ortho-hydroxyphenyl para-quinone methide and γ-butenolides for preparation of chiral 3, 4-dihydrocoumarins","authors":"","doi":"10.1016/j.tetlet.2024.155311","DOIUrl":"10.1016/j.tetlet.2024.155311","url":null,"abstract":"<div><div>A quinine-squaramide catalyzed enantioselective inverse-electron-demand hetero-Diels–Alder reaction between γ-butenolides and <em>ortho</em>-hydroxyphenyl <em>p</em>-QMs has been disclosed. A wide range of chiral 3, 4-dihydrocoumarins frameworks with two adjacent stereogenic centers have been directly and concisely prepared in excellent results (up to 94 % yield, 99:1 dr, 98:2 er) under mild conditions.</div></div>","PeriodicalId":438,"journal":{"name":"Tetrahedron Letters","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142320233","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-25DOI: 10.1016/j.tetlet.2024.155312
A visible-light-induced 6-exo-trig tandem cyclization dearomatization of biaryl ynones with simple ethers was developed. The reaction involves selective C(sp3)H bond cleavage and dual CC bond formation providing efficient, atom and step economical access to alkylated spiro[5.5]trienones under mild conditions.
研究人员开发了一种可见光诱导的双芳基炔酮与单醚的 6-exo-trig 串联环化脱芳烃反应。该反应涉及选择性 C(sp3)H 键裂解和双 CC 键形成，可在温和条件下高效、经济地获得烷基化螺[5.5]三烯酮。
{"title":"Visible-light-induced dual CH functionalization of biaryl ynones via a 6-exo-trig domino radical addition/cyclization/dearomatization: Efficient access to alkylated spiro[5.5] trienones","authors":"","doi":"10.1016/j.tetlet.2024.155312","DOIUrl":"10.1016/j.tetlet.2024.155312","url":null,"abstract":"<div><div>A visible-light-induced 6-exo-trig tandem cyclization dearomatization of biaryl ynones with simple ethers was developed. The reaction involves selective C(sp<sup>3</sup>)<img>H bond cleavage and dual C<img>C bond formation providing efficient, atom and step economical access to alkylated spiro[5.5]trienones under mild conditions.</div></div>","PeriodicalId":438,"journal":{"name":"Tetrahedron Letters","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142417326","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-24DOI: 10.1016/j.tetlet.2024.155313
In this study, we have developed an efficient method for silacycle synthesis using metal hydride hydrogen atom transfer (MHAT) and radical-polar crossover (RPC) mechanism. Allylic silanols were synthesized via one-step condensation and then cyclized under mild conditions using N-fluoropyridinium tetrafluoroborate (Me3NFPY·BF4) as the oxidant under cobalt catalysis. This approach yielded five-, six-, and seven-membered silacycles with high selectivity, with the six-membered rings being the favored products. Density functional theory (DFT) calculations provided valuable insights into the reaction mechanisms and highlighted the role of ring strain in determining product selectivity. This study demonstrated the effectiveness of combining MHAT/RPC methodologies with silicon tethering, thus offering a robust platform for expanding the use of silicon-based strategies in synthetic chemistry.
{"title":"Synthesis of silacycles via metal hydrogen atom transfer and radical-polar crossover mechanism","authors":"","doi":"10.1016/j.tetlet.2024.155313","DOIUrl":"10.1016/j.tetlet.2024.155313","url":null,"abstract":"<div><div>In this study, we have developed an efficient method for silacycle synthesis using metal hydride hydrogen atom transfer (MHAT) and radical-polar crossover (RPC) mechanism. Allylic silanols were synthesized via one-step condensation and then cyclized under mild conditions using <em>N</em>-fluoropyridinium tetrafluoroborate (Me<sub>3</sub>NFPY·BF<sub>4</sub>) as the oxidant under cobalt catalysis. This approach yielded five-, six-, and seven-membered silacycles with high selectivity, with the six-membered rings being the favored products. Density functional theory (DFT) calculations provided valuable insights into the reaction mechanisms and highlighted the role of ring strain in determining product selectivity. This study demonstrated the effectiveness of combining MHAT/RPC methodologies with silicon tethering, thus offering a robust platform for expanding the use of silicon-based strategies in synthetic chemistry.</div></div>","PeriodicalId":438,"journal":{"name":"Tetrahedron Letters","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142328047","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-19DOI: 10.1016/j.tetlet.2024.155309
A visible light-induced pericyclic cascade reaction for the synthesis of eight-membered rings is described. The reaction proceeds via [2 + 2]-photocycloaddition, base-promoted elimination, and retro-4π-electrocyclization. It exhibits broad substrate scope and good functional group tolerance.
{"title":"Visible light-induced pericyclic cascade reaction for the synthesis of eight-membered rings","authors":"","doi":"10.1016/j.tetlet.2024.155309","DOIUrl":"10.1016/j.tetlet.2024.155309","url":null,"abstract":"<div><div>A visible light-induced pericyclic cascade reaction for the synthesis of eight-membered rings is described. The reaction proceeds <em>via</em> [2 + 2]-photocycloaddition, base-promoted elimination, and retro-4π-electrocyclization. It exhibits broad substrate scope and good functional group tolerance.</div></div>","PeriodicalId":438,"journal":{"name":"Tetrahedron Letters","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0040403924004040/pdfft?md5=941608b173ee8fb387c8599daa39a5ee&pid=1-s2.0-S0040403924004040-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142311807","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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