Synthesis-Stuttgart最新文献

Steviol is one of myriad polycyclic terpenoids bearing oxygenation on the axially disposed C19 carbon. The presence of this C19 alcohol renders the C4 quaternary carbon stereogenic, issuing a challenge for stereoselective synthesis. Here we show that a suitably disposed chlorine atom at C2, coupled with the correct diastereomer of terminal epoxide that initiates cationic bicyclization, leads to the desired stereochemical outcome. Subsequently, the anisole terminating group undergoes Birch reduction that simultaneously reduces the C-Cl bond, removing the transient "auxiliary" and completing a short, highly stereoselective formal synthesis of steviol. This work provides another example of the power of removable C-X bonds for stereocontrolled synthesis.

The Nugent-RajanBabu reductive epoxide cyclization has become a mainstay of alternative methods to accomplish classical, biomimetic, cationic polyene cyclizations. In most cases, the regiochemical control for the formation of decalins and perhydrophenanthrenes is exquisite, mirroring that obtained in cationic reactions, to the point where the 6-endo reactivity is anticipated even in the face of potential 5-exo processes. In our studies toward complex, polyoxygenated terpenoid natural products, we had cause to evaluate the reactions of α-alkoxy epoxides in these types of reactions, and we were surprised to uncover a means to control 6-endo vs 5-exo reactions based on the size of the protecting group on the α-oxygen. This knowledge opens up the possibility of rapid syntheses of highly oxygenated cyclopentane systems, in addition to the expected decalin scaffolds.

Herein, we describe a convergent method for the synthesis of benzo-fused cycloheptanones from cyclobutanol derivatives and 1,2-dihaloarene electrophiles. The inherent ring strain of the cyclobutanol coupling partner is leveraged to drive a Pd-catalyzed C-C cleavage/cross-coupling. A subsequent intramolecular enolate arylation results in the formation of the benzo-fused seven-membered carbocycle in a one-pot sequence. A range of electronically diverse 1,2-dihaloarene electrophiles as well as various substituted cyclobutanols were investigated as cross-coupling partners.

Lycopodium alkaloid complanadine A, isolated by Kobayashi et al. in 2000, is a complex and unsymmetrical dimer of lycodine. Biologically, it is a novel and promising lead compound for the development of new treatment for neurodegenerative disorders and persistent pain management. Herein, we reported a concise synthesis of complanadine A using a pyrrole-to-pyridine molecular editing strategy. The use of a nucleophilic pyrrole as the precursor of the desired pyridine enabled an efficient and one-pot construction of the tetracyclic core skeleton of complanadine A and lycodine. The pyrrole group was then converted to a 3-chloropyridine via the Ciamician-Dennstedt one carbon ring expansion. A subsequent C-H arylation between the 3-chloropyridine and a pyridine N-oxide formed the unsymmetrical dimer, which was then advanced to complanadine A. Overall, from a readily available known compound, total synthesis of complanadine A was achieved in 11 steps. The pyrrole-to-pyridine molecular editing strategy enabled us to significantly enhance the overall synthetic efficiency. Additionally, as demonstrated by a Suzuki-Miyaura cross coupling, the 3-chloropyridine product from the Ciamician-Dennstedt rearrangement is amenable for further derivatization, offering an opportunity for simplified analog synthesis.