99474-29-0Relevant academic research and scientific papers
Metal carbene chelates: stable reactive intermediates in cycloaddition reactions
Doetz, Karl Heinz,Popall, Michael,Mueller, Gerhard
, p. 57 - 76 (1987)
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.
Carbene Ligands as Anthracyclinone Synthons, 6. - Metal Carbene Chelates as Key Reagents in Syntheses of the Daunomycinone Series: Regiospecific Annulation of Arylcarbene Ligands as a Strategy towards the Synthesis of Rings B and C
Doetz, Karl Heinz,Popall, Michael
, p. 665 - 672 (2007/10/02)
Reaction of tetracarbonyl carbene chelates of chromium 4, 5, and 18 with terminal alkynes leads to regiospecific annulation of the carbene ligands to give key intermediates in anthracyclinone synthesis.The B-ring of daunomycinone is formed by reaction of 3-(methoxycarbonyl)-5-hexynoate 1 with the naphthylcarbene complexes 4/5.The metal is recycled as hexacarbonylchromium by decomplexation of the anthracenol complexes 6/7 under CO pressure.Conventional steps lead to the tetracyclic systems 14/15 which serve as precursors to daunomycinone C and its 4-demethoxy analogue.The synthesis of ring C involves the annulation of the anisyl complex 18 by the propargylcyclohexanediones 16/17, and - after cleavage of the metal - leads to the naphthol derivatives 21/22.The functionalization of the ketone 23 to give the acid 24 via isocyanomethyl p-tolyl sulfone and the cyclization using TFA/TFAA are key steps towards the tetracyclic diketone 25 which is a well-known precursor of 11-deoxydaunomycinone E.
