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20.5.14.1.5 Method 5: Eschenmoser Sulfide Contraction

DOI: 10.1055/sos-SD-020-01227

Vanderwal, C. D.; Jacobsen, E. N.Science of Synthesis, (2007201326.

The Eschenmoser sulfide contraction is a general and convergent method for the synthesis of 3-aminoalk-2-enoic acid esters and ketones (vinylogous carbamates and amides) from thioamides and α-halocarbonyl compounds. It proceeds by alkylation of the thioamide at sulfur with the halide, and subsequent ring closure to form an episulfide, which is desulfurized with a phosphine or a phosphite. Two examples from complex synthetic efforts are shown in Scheme 22. Thioamides 119 and 121 are converted into 3-aminoalk-2-enoic acid esters 120[‌75‌] and 122,[‌76‌] respectively, in nearly quantitative yields by the ­Eschenmoser reaction.

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