Penicillium spiculisporum

While Lewis acids normally enable l,2-additi(Mis of silyloxy furans to a,(3-unsaturated aldehydes, the MacMillan group discovered that iminium catalysis favors 1,4-additions, thus overcoming the deficiency of normal Lewis acids in Mukaiyama-Michael additions 244). The high potential of this protocol was demonstrated impressively in a short synthesis of the Penicillium spiculisporum fermentation product spiculisporic acid (262). As shown in Scheme 60, vinylogous addition of the silyloxy furan 263 to the acceptor 264 catalyzed by 228 furnished the key intermediate 265 in good enantio- and diastereoselectivity. It is worth noting that the TfOH salt of the catalyst in combination with methyl ester 266 as a Michael acceptor gave the anh-diastereomer 267 exclusively. This compound was then used for the synthesis of 5-epi-spiculisporic acid (268) (Scheme 60) 244). 

Mahlen, A. (1971). Properties of 2-decylcitrate synthase from Penicillium spiculisporum Lehman. Eur. J. Biochem. 22, 104. 

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