The title compounds 2 and 3, which are inhibitors of the biosynthesis of cholesterol, were synthesized in a convergent and perfectly stereoselective manner. In the key step, bromobutenolide 6 (obtained from levulinic acid in two steps) was coupled with either of the novel bis(stannanes) trans,cis,trans-35 or trans,trans,trans-35 [each accessible from 3-(tributylstannyl)allyl alcohol (17) in four steps], giving gamma-alkylidenebutenolide trans,trans,trans-32. This compound was coupled with iododiyne 42 or the bromoenediynoate 44 leading to dihydroxerulin (2) and to the (trimethylsilylethyl)ester 45 of xerulinic acid, respectively. Deprotection of the latter provided totally synthetic xerulinic acid (3) for the first time.

Interest in the synthesis of the C(23)-C(40) fragment 2 of tetrafibricin prompted us to develop a new method for the synthesis of 1,5-syn-(E)-diols. Toward this end, the kinetically controlled hydroboration of allenes 6, 33, ent-39, 42 and 45 with the Soderquist borane 25R were studied. Tetrabutylammonium allenyltrifluoroborate 45 gave superior results and was utilized in a double allylboration sequence with two different aldehydes to provide the targeted 1,5-syn-(E)-diols in generally high yields (72–98%), and with high enantioselectivity (>95% e.e.), diastereoselectivity (d.r. >20:1), and (E)/(Z) selectivity (>20:1). This new method was applied to the synthesis of the C(23)-C(40) fragment 2 of tetrafibricin.

A highly stereoselective synthesis of (E)-1,5-syn-diols 6 is described. The kinetically controlled hydroboration of allenyltrifluoroborate 8 with Soderquist borane 2 provides the (Z)-allylic trifluoroborate 9, which undergoes sequential allylboration with two different aldehydes to provide (E)-1,5-syn-diols 6 in 72–98% yields with > 95% ee. and > 20:1 dr. Application of this method to the synthesis of the tetrafibricin C(23)-C(40) fragment 19 is described.

Stereoselective syntheses of 1,6-bis(tributylstannyl)hexa-1,3,5-trienes, 1,8-bis(tributylstannyl)octa-1,3,5,7-tetraenes, and 1,10-bis(tributylstannyl)deca-1,3,5,7,9-pentaenes with various methylation patterns were achieved based on stereocomplementary C=C bond-forming reactions. All-E isomers resulted from Ramberg-Bäcklund rearrangements of distannylated diallyl-, allylpentadienyl-, or bis- (pentadienyl)sulfones. Mono-Z-configured 1,ω-bis(tributylstannyl)-1,3,5-polyenes emerged from (Sylvestre-)Julia olefinations of Bu(3)Sn-substituted enals or dienals with Bu(3)Sn-substituted allyl or pentadienyl benzothiazolylsulfones. Related Ramberg-Bäcklund approaches provided all-E-1-bromo-6-(tributylstannyl)hexa-1,3,5-triene but not all-E-1-(tetramethyldioxaborolanyl)-6-(tributylstannyl)hexa-1,3,5-triene.

An inhibitor of the biosynthesis of cholesterol, xerulinic acid, has been synthesized for the first time. The convergent approach applied involves the palladium‐catalyzed coupling of an enediynoic ester building block, a conjunctive C6 bisstannane, and a bromine‐containing methylenebutenolide (see scheme; R=Me3SiCH2CH2).