Deoxygenation of Oxiranes by λ3σ3‐Phosphorus Reagents: A Computational, Mechanistic, and Stereochemical Study

Abstract

AbstractThe deoxygenation of parent and substituted oxiranes by λ3σ3‐phosphorus reagents has been explored in detail, therefore unveiling mechanistic aspects as well as regio‐ and stereochemical consequences. Attack to a ring C atom is almost always preferred over one‐step deoxygenation by direct P‐to‐O attack. In most cases a carbene transfer occurs as first step, leading to a phosphorane and a carbonyl unit that thereafter react in the usual Wittig fashion via the corresponding λ5σ5‐1,2‐oxaphosphetane intermediate. Betaines rarely constitute true minima after the first C‐attack to oxiranes, at least in the gas‐phase. Use of the heavier derivatives AsMe3 and SbMe3 as oxirane deoxygenating reagents was also mechanistically studied. The thermodynamic tendency of λ3σ3‐phosphorus reagents to act as oxygen (O‐attack) or carbene acceptors (C‐attack) was theoretically studied by means of the thermodynamic oxygen‐transfer potential (TOP) and the newly defined thermodynamic carbene‐transfer potential (TCP) parameters, that were explored in a wider context together with many other acceptor centres.