Trimethylsilyl-Substituted Propyne Iminium Salts as Building Blocks in [4+2] Cycloaddition Reactions

Abstract

3-(Trimethylsilyl)propyne iminium salts 6a-c and 2-(trimethylsilyl)ethynyl-1,3-benzothiazolium triflate 12 are suitable dienophiles for Diels-Alder reactions with buta-1,3-dienes, cyclopentadiene, cyclohexa-1,3-diene, and anthracene. Tri-tert-butylazete reacts with propyne iminium salts 6a,b to form Dewar­pyridines 15a,b. Thermal isomerization of 15b generates the sterically overcrowded pentasubstituted pyridine 16 which features a boat-shaped pyridine ring with the highest deviation from planarity so far reported.