Carbonylativecycloaddition of allyl tosylates and alkynes proceeded in the presence of palladium catalysts to afford a range of cyclopentenones. In the presence of methanol, five-component coupling reactions gave methyl cyclopentenyl acetates, whereas in the absence of methanol, (cyclopentenoylmethylidene)furanones were formed from six components. Allyl tosylate was found to be essential for these
Ni-promoted Cyclopentenone Formation by Intramolecular Cyclocarbonylation of 1-Bromo-1,4-dienes
作者:Amadeu Llebaria、Francisco Camps、Josep Ma Moretó
DOI:10.1016/s0040-4020(01)85818-x
日期:1993.2
the formation of 1-bromo-1,4-dienes which were further converted to cyclopentenones through a Ni(CO)4 promoted carbonylation-cyclization process. Four CC bonds are formed by this two step sequence, leading to 2,3-substituted 5-methoxycarbonylmethylcyclopentenones 1. Application of this procedure to 2-butyne affords cyclopentenone 1c, an immediate precursor of the antibiotic methylenomicyn B.
A new synthesis of methylenomycin B (1) has been accomplished in four steps starting with a NI(CO)4 promoted cyclocondensation reaction of allyl chloride and 2-butyn-1-ol in MeOH, followed by hydrogenolysis of the resulting mixture to 2,3-dimethyl-5-methyl-oxycarbonylmethyl-2-cyclopentenone (3), which by hydrolysis and oxidative decarboxylation yielded 1.