Reductive lithiation of sulfur-containing heterocycles with aromatic radical anions: Synthetic applications

2H-3,4-dihydro-1-benzothiopyran, 1, and 2,3-dihydrobenzothiophene, 8, have been reductively cleaved by lithium 4,4'-di-tert-butylbiphenylide (LDBB) to the dianions 2 and 9, respectively. The dianion 2 can be captured with MeOD to give the deuteriated compound 3 and with carbonyl compounds to give the hydroxyalkylbenzenethiols 4a-e, which in turn have been cyclized to the tetrahydrobenzothiepins 5a-e. Similarly, the dianion 9 reacts with MeOD furnishing 10 and with carbonyl compounds yielding the hydroxyalkylbenzenethiols 11. Benzenethiol 11a has been cyclized to the thiochromane 12. The reductive lithiation of 2,2,3-trimethylbenzothiazoline, 13, generates the ''unstabilized'' alpha-amino tertiary carbanion 14, which has been trapped with a number of electrophiles to give the products 15, 16, 19, 20 and 23-25.