Reversible P(III)/P(V) Redox: Catalytic Aza‐Wittig Reaction for the Synthesis of 4(3 H )‐Quinazolinones and the Natural Product Vasicinone

The catalytic aza‐Wittig reaction based on a phosphine/phosphine oxide catalytic cycle is reported. The by‐product triphenylphosphine oxide (Ph 3 PO) was reduced in situ to triphenylphosphine (Ph 3 P) with good chemselectivity so that the aza‐Wittig reaction can be accomplished by using merely a catalytic amount of triphenylphosphine. The reaction has been demonstrated in an efficient synthesis of 4(3 H )‐quinazolinones and the natural product ( S )‐vasicinone in high yields, by using a catalytic amount of triphenylphosphine (5%) and the tetramethyldisiloxane/titanium tetraisopropoxide [TMDS/Ti(O‐ i‐ Pr) 4 ] reductant system (81–95% yields and >99% ee ).