Group 6 Pyrrolocarbene Complexes as Alkoxycarbene Complex Analogs
摘要:
Chromium, molybdenum, and tungsten carbene complexes;having the pyrrole group as the heteroatom-containing substituent were synthesized and characterized. Their thermal and photochemical reactivity more nearly resembled that of alkoxycarbene complexes than that of aminocarbene complexes. Thus, they cyclopropanated electron deficient olefins, produced hydroquinones rather than indenes in the Dotz annulation process, and underwent photochemical 2 + 2 cycloaddition with alkenes to produce cyclobutanones and with imines to produce beta-lactams. With cyclohexadiene and cycloheptadiene, an unusual 4 + 2 cycloaddition of the diene across the ketene carbonyl group was observed. The pyrrole group was oxidatively cleaved to the corresponding formamide, the hydrolysis of which gave the free NH2 group, making the pyrrole group functionally equivalent to the amino group.