Twofold Extrusion Reactions

Abstract

Twofold extrusion reactions are chemical transformations in which two small inorganic molecules or atoms connecting carbon or nitrogen atoms are lost, generating the corresponding carbon-carbon or carbon-nitrogen double bonds. These reactions are particularly useful for the preparation of sterically hindered alkenes and imines. The inorganic species liberated in twofold extrusion reactions can be molecular nitrogen, sulfur, selenium, tellurium, sulfur dioxide, sulfur monoxide, carbon dioxide or carbon monoxide. The most common precursors for twofold extrusion reactions are 1,3,4-thiadiazolines, which thermally extrude molecular nitrogen affording thiiranes. These thiiranes can be readily desulfurized to afford the corresponding alkenes using tertiary phosphines. The corresponding 1,3,4-selenadiazolines thermally extrude both molecular nitrogen and atomic selenium directly affording alkenes. Alkenes can also be prepared by formal extrusions of molecular nitrogen plus sulfur dioxide or sulfur monoxide. Extremely sterically hindered imines can be prepared by extrusions of molecular nitrogen and sulfur or selenium from in situ generated heterocyclic precursors. Other less common twofold extrusion reactions are also reported. The detailed preparations of the required precursors for the twofold extrusion reactions as well as the mechanisms of these extrusion processes are discussed in this chapter. The utility of twofold extrusion reactions in the preparations of ‘molecular rotors’ and other extremely sterically hindered alkenes is presented. The steric limitations of the twofold extrusion reactions are discussed along with comparisons of these reactions with other alkene- and imine-forming synthetic methods. The Tabular Survey covers material through the end of 2009. Keywords: Extrusion; twofold extrusion; alkene; imine; 1,3,4-thiadiazolines; 1,3,4-selenadiazolines; [nitrogen, sulfur, selenium, tellurium, sulfur dioxide, sulfur monoxide, carbon dioxide and carbon monoxide (all with extrusion)]; thiocarbonyl ylide; tertiary phosphine; diazo compounds; thiones; selones; sulfenes; selenirane; azines; chelotropic extrusion; Barton-Kellogg reaction; Staudinger-Pfenninger reaction; Schonberg reaction; thiadiazoline-1,1-dioxides; thiirane 1,1-dioxide; thiirane 1-oxide; oxathiolan-4-ones; lead tetraacetate; barium manganate; diselenium dibromide; thiocarbonyl-S-imide; copper powder; photochemical extrusion; flash vacuum pyrolysis (FVP); rhodium (II) acetate; 1,3-dithiacyclopentanes; hydrazones; thiaziridine 1,1-dioxides; p-toluenesulfonylhydrazones; 1,2,3-thiadiazolines; alkenes (sterically hindered); imines (sterically hindered); N-sulfonylamines; retrocyclization; iminium salts (sterically hindered); geminal dihalides; nanoscale devices; photonic devices; thiophosgene; O-thioesters; O-selenoesters; enol ethers; dithioesters; thioenol ethers; thionolactones; thioamides; thiolactams; trithiocarbonates; ketene thioacetals; thioacyl halides; thionitroso compounds; thiatriazoline; trimethyl orthoformate; hydrogen sulfide; triphenylphosphoranylidene hydrazones