Total synthesis of -eremantholide

Carbocyclization of a radical derived from butyrolactone 91 onto an alkyne under reductive conditions gave the bicyclic lactone 92 in moderate yield [95JOC8179]. This intermediate was used m the total synthesis of (+)-eremantholide A 93. 

In 1991 Boeckman and co-workers reported the total synthesis of (+)-eremantholide A (8), as the natural enantiomer [28]. For construction of... 

In 1995 we accomplished the total synthesis of (+)-eremantholide A (8). Our synthetic scheme was completely different from that of the Boeckman group. We selected our building block 2 as the starting material, and the retrosynthetic analysis is outlined in Scheme 6. At first, disconnection of two carbon-carbon bonds in 8 as depicted leads to two fragments, an A/B ring equivalent 55 and known disubstituted 3(2if)-furanone derivative 56. We planned the direct connection of intact 3(2if)-furanone 56 to 55 at a... 

A number of oxacyclic natural products were synthesized via carbocycle-forming radical reaction of oxacyclic intermediates. An early example is the synthesis of (-)-dihydroagarofuran (170) by Biichi [109] (Scheme 58). The bridgehead chloride 168 obtained from the corresponding hydroxy ketone was amenable to radical cycliza-tion, and the tricyclic ether 169 was duly obtained. The aplysin synthesis [110] provides another example, and (—)-karahana ether (173) was synthesized via radical cyclization of the substrate 171 [111] (Scheme 59). Lactonic natural products (-1-)-eremantholide A [112], alliacolide [113], and (-)-anastrephin [114] were prepared via a variety of carbocycle-forming radical cyclization reactions. In the total synthesis of spongian-16-one (176) [115] (Scheme 60), the butenolide moiety in the substrate 174 served as the final radical acceptor for three consecutive 6-endo-. rig cyclizations. 

In a study on the biosynthesis of the polyether antibiotic lasalocid A, a syn-selective Evans aldol reaction of 83 with methacrolein gave 84 in 95% isolated yield. In the total synthesis of the antitumor sesquiterpenoid (+)-eremantholide A, an Evans aldol reaction was used to deliver a single syn-... 

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