Cyclopropyl building blocks in organic synthesis, part 143. A two-step, three-component queuing cascade leading to dihydrobenzoxepine and dihydrobenzazepine derivatives

Abstract

A palladium-catalyzed reaction of methylenespiropentane (11) with iodobenzene (12) under typical Heck conditions [Pd(OAC)(2), PPh3, Et3N, DMF] produced a mixture of the unstable [3]dendralene 13 and allylidenecyclopropane 14 in 38 % yield. When an analogous reaction with iodobenzene was carried out in the presence of morpholine (25) and of tris(2-furyl)phosphane (TFP) instead of triphenylphosphane, the dienes 26, 28 and 31 were generated by nucleophilic trapping of pi-allylpalladium intermediates 30 and 32. The cross coupling of methylenespiropentane (11) with the functionalized aryl iodides 33a-g in the presence of a palladium precatalyst [Pd(OAc)2, TFP, Et3N, DMF] at 80 degrees C, 3 h, provided the seven-membered 3,4-dimethylene-substituted heterocycles 34a-g and 35b which, upon addition of dimethyl fumarate (19), underwent Diels-Alder reactions to furnish bicyclic and higher oligocyclic dihydrobenzoxepine and -benzazepine derivatives 36a-g and 37b, yet in rather moderate yields of 18-29 % only. The overall process constitutes a one-pot, two-step, three-component queuing cascade. (