BIFUNCTIONAL CHIRAL AUXILIARIES .7. ALDOL REACTIONS OF ENOLATES DERIVED FROM 1,3-DIACYLIMIDAZOLIDINE-2-THIONES AND 1,3-DIACYLIMIDAZOLIDIN-2-ONES

Dibutylboron enolates of 1,3-diacylimidazolidine-2-thiones and 1,3-dia cylimidazolidin-2-ones undergo highly syn-stereoselective aldol reacti ons with aldehydes to allow elaboration of both acyl sidechains. The r eaction is proposed to occur via sequential enolisation rather than vi a a bisenolate and the stereochemistry of the product was elucidated b y both X-ray crystallography and reductive cleavage of a homochiral al dol product to give (1R,2S)-1-phenyl-2-methylpropane-1,3-diol. In cont rast, tin (II) triflate mediated aldol reactions result in only one of the two acyl sidechains reacting and exhibit reversed enantiofacial s tereoselectivity.