A case of highly diastereoselective addition to unsymmetrical ketones: lk‐addition of (2‐alkenyl)triphenoxytitanium derivatives

Abstract (2‐Butenyl)‐, (4‐methyl‐2‐pentenyl)‐, and (2‐heptenyl)triphenoxytitanium (2a–c) add to dialkyl, alkyl aryl‐, and alkinyl aryl ketones to give high yields of tertiary homoallylic alcohols (5–12), which are diastereomerically enriched up to 98%. Configurational assignment by degradation of two of the products to olefins 15 and 18 ‐ through β‐hydroxy acids 13 and 16 and β‐lactones 14 and 17 ‐ leads to the proposal of a general mechanism and of a specification of the relative topicity lk of the process (Scheme 5). The allylic Ti‐compounds 2 can serve as d2‐reagents (see the d2‐synthon II and the aldol‐type structures 1).