Ring Expansion of 1,2,3,4-Tetrahydroisoquinolines to Dibenzo[c,f ]azonines. An Unexpected [1,4]-Sigmatropic Rearrangement of Nitrile-Stabilized Ammonium Ylides

摘要

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.