How To Tune Acid‐Induced Ring Enlargement Reactions – The Strange Case of 2H‐Azaphosphirene Complexes and Its Surprising Dichotomy

Abstract 2H‐Azaphosphirene complex 1a reacted with TfOH, cyclohexyl isocyanide, and subsequently with NEt3 – P–N‐bond‐selectively – to give the first 2,3‐dihydro‐1,3‐azaphosphete complex 2. Under the same conditions, 2H‐azaphosphirene complex 1b underwent a P–C‐bond‐selective ring enlargement with phenylacetylene with formation of 2H‐1,2‐azaphosphole complex 3. Apart from X‐ray crystallographic data (2, 3), DFT calculations are discussed, which provide first insight into this surprising dichotomy.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)