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Metal carbene chelates: stable reactive intermediates in cycloaddition reactions

1987; Elsevier BV; Volume: 334; Issue: 1-2 Linguagem: Inglês

10.1016/0022-328x(87)80038-4

1872-8561

Karl Heinz Dötz, Michael Popall, Gerhard Müller,

N-Heterocyclic Carbenes in Organic and Inorganic Chemistry

Carbonylcarbene complexes bearing either heteroatoms or CC bonds in a carbene γ-position are susceptible towards facile decarbonylation. The coordination of the additional donor group affords stable five-membered metal carbene chelates. Olefin-chelated metallacycles are obtained via aminolysis of alkoxy carbene complexes using allylamine. Heteroatom metal carbene chelates are accessible from ortho-lithiated methoxyarenes in a two-step process involving a sequential nucleophile/electrophile addition to metal carbonyls followed by thermal decarbonylation. Both types of compounds have been studied systematically by X-ray analysis. The characteristic feature of oxametallacycles is a long metal to oxygen bond. The ready ring-opening is exploited in the carbene annulation reaction in which now the ligand coupling can be separated from the generation of a vacant coordination site at the metal template. The scope of this strategy is demonstrated by two approaches to anthracyclinones: Either ring B or C can be formed from 1,4-dimethoxy-2-naphthylcarbene or anisylcarbene synthons.