Up to seven-component adducts by unprecedented multiple alkyne and carbonyl insertions in the metal-carbon bond of chromium alkoxy alkynyl carbene complexes

Chromium alkoxy alkynyl Fischer carbene complexes react with symmetrical internal alkynes to form new and different organometallic species, which result from consecutive insertions of several alkyne units and carbonyl groups into the metal-carbon bond. The insertion sequence can be controlled and, by slight modification of the reaction conditions, it can be directed to the preparation of either seven- or five-component adducts. Three molecules of alkyne, two carbonyl groups, the carbene ligand and the chromium metal moiety partake in the creation of seven new carbon-carbon bonds and two five-membered carbocycles in the first case while four new carbon-carbon bonds, a sigma Cr-C(sp(2)) bond and a cyclopentadienyl moiety are built in the second case. Evidence that five-component chromium complexes are intermediates in the formation of seven-component adducts is provided; they are also able to insert a unit of a different internal alkyne which confers more diversity to the seven-component adducts. The presence of the sigma Cl-C(Sp(2)) bond has also been exploited to develop the synthesis of both cyclopentene-fused and novel spiro-cyclopenten ones as well as symmetrical biscyclopentenones. Finally, the isolation of six-component adducts, when tolane was employed as the initial alkyne, provides further support to the proposed mechanism.