Diastereoselective diazenyl formation: the key for manganese-catalysed alcohol conversion into (E)-alkenes

Abstract

The proposed reaction mechanism for the unprecedented direct transformation of primary alcohols into alkenes catalysed by Mn(I)-PNP complexes consists of two cycles. First, the acceptorless dehydrogenation of the alcohol into aldehyde is produced via a concerted mechanism. Secondly, in an excess of hydrazine, hydrazone is formed and reacts with the aldehyde to produce olefins. This process, taking place in base-free conditions, is characterised by the diastereoselective formation of diazenyl intermediates. Based on DFT data, the generation of the (S_N,S,S) diastereoisomer is favoured over the rest, leading in its decomposition to the preferential formation of an (E)-alkene and liberating N₂ and H₂O as the only by-products.