Aldehydes, olefinic from acyl chlorides

When jS-hydrogens are present in the substrate aldehyde, olefins and H2 are produced, but in substantially smaller quantities than observed with analogous acid chlorides. For example, decarbonylation of heptanal yields 14% hexene, whereas exclusive formation of alkene is observed from similar acyl chlorides. This difference is due to the ease with which hydride transfer (as opposed to chloride transfer) occurs in the respective alkyl intermediates. 

A library of highly functionalized pyrrolidines was prepared from resin-bound azomethine ylides and electron-deficient olefins (Scheme 11.7). Four amino acids, four aldehydes, five olefins, and three acyl chlorides were used as building blocks to produce a library of diverse cycloadducts for various enzymatic assays. Ester-linked products were cleaved from TentaGel or SASRIN resins as carboxylic acids with diluted trifluoroacetic acid. Structural diversity of the proline derivatives was enhanced with iV-acylation of the pyrrolidines. 

On the pages which follow, general methods are illustrated for the synthesis of a wide variety of classes of organic compounds including acyl isocyanates (from amides and oxalyl chloride p. 16), epoxides (from reductive coupling of aromatic aldehydes by hexamethylphosphorous triamide p. 31), a-fluoro acids (from 1-alkenes p. 37), 0-lactams (from olefins and chlorosulfonyl isocyanate p. 51), 1 y3,5-triketones (from dianions of 1,3-diketones and esters p. 57), sulfinate esters (from disulfides, alcohols, and lead tetraacetate p. 62), carboxylic acids (from carbonylation of alcohols or olefins via carbonium-ion intermediates p. 72), sulfoxides (from sulfides and sodium periodate p. 78), carbazoles... 

The synthesis of the Cl-Cl5 segment (116) [198] of streptovaricin D (109) has been carried out from the aldehyde (115) [199], an enantiomer of an intermediate used by the same authors in the synthesis of the rifamycin ansa chain. Compound (105) was submitted to the Evans aldol procedure to give an aldol, which was transformed into the corresponding acetonide. Ozonolysis to the expected aldehyde and crotylmetallation with chromium(II) chloride provided a 5 1 mixture of diastereoisomers. The major component was acylated, giving only one diastereoisomer after ozonolysis and crotylboration. Final introduction of the corresponding (2 ,4Z)-dienoate unit by two subsequent Horner-Wadsworth-Emmons olefinations afforded compound (116) (Scheme 51). 

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