The interest in carbenoids as useful intermediates for organic synthesis has recently grown a great deal.1-2 In contrast to many kinds of 'carbenoids' , free alkylidene 'carbenes' have not been as widely accepted as valuable species for the synthesis of natural products, although their generation by various methods and attractive reactions have been reported.3.4 Typical reactions of alkylidene carbenes are: intramolecular C-H insertion that leads to cyclopentene formation (reaction A in Scheme 1); intermolecular 0-H insertion with an alcohol that gives an enol ether (reaction B); and Fritsh-Buttenberg-Wiechell rearrangement that produces a terminal alkyne (reaction C). Reported here is a chiral synthesis of (-)-malyngolide 1,s an antibiotic from a bluegreen alga,6 using all three of these reactions.The cyclopentene 3 was prepared through intermolecular C-H insertion of the alkylidene carbene, which was generated
Novel Synthesis of (-)-Malyngolide Using Reactions of Alkylidene Carbenes.-A full step synthesis of (-)-malyngolide (X) and its epimer (XI) is presented. The formation of compounds (III) and (VII) proceeds via an alkylidene carbene biradical mechanism. -(OHIRA, S.; MORITANI, M.; IDA, T.; YAMATO, M.; J.
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Synthesis of (-)-Malyngolide Using Reactions of Alkylidenecarbenes.-Via the alkylidenecarbene intermediates in the transformations to (V) and (X) as key steps the title compound (-)-(XV) is synthesized. In the final step 81% of the starting material is recovered. By repeating this reaction four times 45% yield of (-)-(XV) and its epimer (XVI) is obtained. Other approaches from (XII) to the final product are also discussed. -(OHIRA, S.; IDA, T.; MORITANI, M.; HASEGAWA, T.; J. Chem. Soc.
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