Stereochemical Studies. XXIII. Stereochemistry of the Thermal Isocyanide-Cyanide Rearrangement

Abstract

Thermal rearrangements of R(+)-2-(2-carboethoxy-1-phenyl) propyl isocyanide (R(+)-VIII), S(+)-2-(2-methyl-1-phenyl) butyl isocyanide (S(+)-XVI) and R(+)-2-(2-phenyl) butyl isocyanide (R(+)-XXVIII), were carried out under several reaction conditions. Although the reflux of a diphenyl ether solution of R (+)-VIII or heating R(+)-VIII without solvent afforded almost completely racemized cyanide (S (+)-X) (at most 9% retention of configuration) as the sole reaction product in excellent yields, treatment of S (+)-XVI with a procedure similar to that used with R (+)-VIII gave S (+)-cyanide (S (+)-XXIII) with 90% (reflux of a diphenyl ether solution) and 47% (heating without solvent) retention of configuration. The thermal reaction of R(+)-XXVIII gave three different olefins (XXXIV, XXXV, and XXXVI), in addition to the normal reaction product (R(+)-XXIX) with a low retention of configuration (at most 19%). These observations were discussed from various aspects including the effect of asymmetric solvation due to diphenyl ether and the relative stability of the radical intermediates formed.