STEREOCONTROLLED THIO-CLAISEN REARRANGEMENT OF S-ALLYLIC KETENE AMINOTHIOACETALS BY AN HYDROXYSUBSTITUTED ADJACENT STEREOGENIC CENTER

(Z)-S-allylic ketene aminothioacetals were prepared from N,N-Dimethyl beta-hydroxythioamides 2-8 by deprotonation with LDA (2 eq.) at -78 de grees C followed by S-alkylation with allylic bromide. Rearrangement o f these compounds occured easily at room temperature affording major s yn N,N-dimethyl beta-hydroxy alpha-allylic thioamides 9-21 with a syn/ anti ratio of 80/20 to 98/2. The syn configuration of the major diaste reoisomer was confirmed by an univocal synthesis of syn thioamides 9 a nd 11. The structure assignments were confirmed by empirical C-13 NMR rules. The observed induction is well supported by a proposed transiti on state model. (C) 1997 Elsevier Science Ltd.