Zur Reaktion von Dialkylphosphiten mit α‐Enonen, I Synthese und Allyl‐Umlagerung von (1‐Hydroxy‐2‐alkenyl)‐ und (1‐Hydroxy‐2‐cycloalkenyl)phosphonsäure‐dimethylestern

Reaction of Dialkyl Phosphites with α‐Enones, I. – Synthesis and Allylic Rearrangement of Dimethyl (1‐Hydroxy‐2‐alkenyl)‐ and (1‐Hydroxy‐2‐cycloalkenyl)phosphonates Various β,γ‐unsaturated α‐hydroxyphosphonates 3 are prepared in good yields by NaOCH3‐catalyzed regioselective 1,2‐addition of dimethyl phosphite to acyclic and cyclic α‐enones at −35°C. On acid‐catalyzed acetylation, the allylic α‐hydroxyphosphonates 3 (R1, R2 + H) rearrange under thermodynamic control; yielding the new 3‐acetyloxy‐1‐(cyclo)alkenyl derivatives 8, from which the transposed allylic alcohols 11 are readily obtained. Using shorter reaction times, acetylation of compounds 3 affords mixtures of 1‐ and 3‐acetylated products, 10 and 8, respectively.