Sodium amalgam stereoselectivity

This synthetic sequence for an olefin synthesis has been further developed by Kocienski who has shown that eliminative desulphonylations carried out on / -acyloxysulphones are remarkably stereoselective for the synthesis of trans-disubstituted-olefins. The method has wide applicability in that a-lithio phenyl sulphones are readily generated, and are readily coupled to aldehydes or ketones, to give j8-hydroxysulphones. The hydroxyl function of these is then esterified and the synthesis is completed by the reductive elimination with sodium amalgam. Kocienski has prepared two reviews that summarize his syntheses of a range of natural products - one of which is diumycinoP obtained... 

Reductive elimination with sodium amalgam was used in a recent synthesis of diumycinol (4) to introduce two of the hindered double bonds. Thus, this reaction was successful in converting 1 to 2 when alternative methods failed and in introducing the rroas-double bond of 4 more stereoselectively than other methods tried.3... 

A different approach to 2-aUcenylanilines makes use of benzoth-iazines derived from the reaction of 1 with alkynes. Reduction of these compounds with sodium amalgam leads directly to the product anilines. Interestingly, for those systems examined which could produce geometrical isomers, these were formed with good-to-exceUent stereoselectivity, in aU cases favoring the Z-isomers (eq 11). 

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