Ring expansion of 1,2,3,4-tetrahydroisoquinolines to dibenzo[c,f]azonines. An unexpected [1,4]-sigmatropic rearrangement of nitrile-stabilized ammonium ylides.
When the products of a Strecker reaction of 1,2,3,4-tetrahydroisoquinolines with aromatic aldehydes are quaternized with alkyl triflates and subsequently treated with base, a ring expansion to 6,7,8,13-tetrahydro-5H-dibenzo[c,f]azonine-5-carbonitriles takes place. The nine-membered cyclic products can be obtained in good yields (78-89%) in a process involving the [1,4]-sigmatropic rearrangement of a nitrile-stabilized ammonium ylide. The reaction sequence provides a new, simple, and efficient method for the synthesis of these unusual N-heterocycles.
Institute of Organic Chemistry, University of Mainz , Duesbergweg 10-14, D-55128 Mainz, Germany.
Julio Cesar
JC
Orejarena Pacheco
Till
T
Opatz