Stereocontrolled Thio-Claisen rearrangement of S-allylic ketene aminothioacetals by an hydroxysubstituted adjacent stereogenic centre

Article abstract of DOI:10.1016/S0040-4020(97)10178-8

(Z)-S-alkylic ketene aminothioacetals were prepared from N,N-Dimethyl β-hydroxythioamides 2-8 by deprotonation with LDA (2 eq.) at -78°C followed by S-alkylation with allylic bromide. Rearrangement of these compounds occured easily at room temperature affording major syn N,N-dimethyl β-hydroxy α-allylic thioamides 9-21 with a syn/anti ratio of 80/20 to 98/2. The syn configuration of the major diastereoisomer was confirmed by an univocal synthesis of syn thioamides 9 and 11. The structure assignments were confirmed by empirical ¹³C NMR rules. The observed induction is well suppported by a proposed transition state model.