Metal carbene chelates: stable reactive intermediates in cycloaddition reactions

Article abstract of DOI:10.1016/0022-328X(87)80038-4

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 ring C can be formed from 1,4-dimethoxy-2-naphtylcarbene or anisylcarbene synthons.