ChemInform Abstract: Cycloadditions of 1‐Aza‐2‐azoniaallene Ions to Alkenes.

Abstract

Cycloadditions of 1-Aza-2-azoniaallene Ions to Alkenes.-Treatment of chloroazo compounds such as (I), (VII), and (XIII) with Lewis acids (SbCl 5 , AlCl 3 , SnCl 4 , TiCl 4 ) in the presence of ethene or mono-to trisubstituted electron-rich alkenes generates in situ 1-aza-2-azoniaallene salts which undergo cycloaddition to the alkenes. These cycloadditions proceed with complete Markovnikov regioselectivity and retention of the configuration of the alkene. For cycloadducts with a hydrogen atom in the 5-position such as (III), tautomerization in solution to the 1H-pyrazolium salts is observed. For norbornene cycloadduct (XIX) a Wagner-Meerwein rearrangement to the 1Hisomer (XX) occurs in solution. The twofold cycloaddition to norbornadiene also proceeds with exo, exo orientation. The mechanistic proposals are supported by AM 1 calculations. -(WIRSCHUN, WOLFGANG G.; AL-SOUD, YASEEN A.; NUSSER, KONSTANZE A.; ORAMA, OLLI; MAIER, GERD-MICHAEL; JOCHIMS, JOHANNES C.; Perkin 1 (2000) 24, 4356-4365;