Mn(III)-Mediated Synthesis of Pyridines

Significance

Reported here is the Mn(III)-mediated synthesis of pyridines 3 from vinyl azides 1 and cyclopropanols 2. Sub-stoichiometric amounts of Mn(acac)₃ may be used in the reaction, although an oxidant such as DDQ or molecular O₂ must be added. Ultimately, the use of excess Mn(acac)₃ led to higher yields and increased operational simplicity. Alkyl-, aryl-, heteroaryl-, alkenyl- and alkynyl-substituted pyridines may all be prepared ­using this methodology. When bicyclic cyclo-propanols 5 were used as substrates under catalytic Mn(III) conditions, 2-azabicyclo[3.3.1]non-2-en-1-ols 6 were formed in excellent yields in most cases. A radical cyclization mechanism is proposed without experimental evidence.