Several b-unsubstituted (Z)-g-alkylidenebutenolides have been prepared in highly stereocontrolled fashion by implementing a steric directing group stratagem in the vinylogous aldol condensation of butenolides with aldehydes. Applications to the synthesis of the antitumor heptene (S)-melodorinol and a thiophenelactone from Chamaemelum nobile L. are described.
A New, Highly Stereoselective Synthesis of β-Unsubstituted (Z)-γ-Alkylidenebutenolides Using Bromine as a Removable Stereocontrol Element. -Vinylogous aldol condensation of β-bromobutenolides (I) and (V) with various aldehydes followed by β-elimination in the presence of DBU or MesCl proceeds with excellent stereoselectivity to furnish (Z)-γ-alkylidenebutenolides. Reductive debromination provides β-unsubstituted (Z)-γ-alkylidenebutenolides, which are otherwise hardly obtained, in good yields and as single stereoisomers. The synthetic utility of this approach is demonstrated the synthesis of butenolide (XIII), a key intermediate in the synthesis of the antitumor agent melodorinol. -(BOUKOUVALAS*, J.; BELTRAN, P. P.; LACHANCE, N.; COTE, S.; MALTAIS, F.; POULIOT, M.; Synlett 2007, 2, 219-222; Dep. Chim., Univ. Laval, Laval, Que. G1K 7P4, Can.; Eng.) -Mischke 25-097
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