REARRANGEMENTS OF 1,6,7-TRISUBSTITUTED 2-METHYL-1,2,3,4-TETRAHYDROISOQUINOLINIUM 2-METHYLIDES

Chemical behavior of 1,6,7-trisubstituted 2-methyl-1,2,3,4-tetrahydroisoquinolinium 2-methylides 4 was investigated in fluoride-ion induced desilylation reaction of 1,6,7-trisubstituted 2-methyl-2-(trimethylsilyl)-methyl-1,2,3,4-tetrahydroisoquinolinium iodides 3. The 1-nonsubstituted (4a,b) and 1-alkyl-substituted ylides (4c,d) gave mixtures of five products (7-11), but the 1-phenyl-substituted analogues (4e,f) yielded (E)- and (Z)-2,3-disubstituted 5-benzylidene-1,3-cyclohexadiene-6-spiro-3'-1'-methylpyrrolidines (E)-5 and (Z)-5 and 7,8-disubstituted 3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepines 6. The mechanisms of the rearrangement are discussed.