A Two‐Step, Three‐Component Queuing Cascade Leading to Dihydrobenzoxepine and Dihydrobenzazepine Derivatives

A palladium‐catalyzed reaction of methylenespiropentane ( 11 ) with iodobenzene ( 12 ) under typical Heck conditions [Pd(OAc) 2 , PPh 3 , Et 3 N, 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 π‐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, Et 3 N, DMF] at 80 °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.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)