The low KEnol values of β-sulfonyl-substituted amides

Abstract

Amides substituted by one β-sulfonyl group and another β-sulfonyl, β-ester or β-CN group, form very low percentages of the corresponding enols, lower than for the β,β-diester and β-cyano, β-ester substituted systems, despite the equal or weaker electron delocalizing ability of the latter groups which help to stabilize the enols more than that of the sulfonyl group. This cannot be attributed to the non-planarity of the enols, since the calculated structures are planar. It is suggested that the sulfonyl-substituted amides are more stabilized than the β-ester-or β-cyanosubstituted amides. An amide substituted by β−nonafluorosulfonyl, β−acetyl groups enolizes on the acetyl group, forming a strong, nearly symmetrical intramolecular hydrogen bond. The use of 600 MHz NMR spectroscopy can extend the range of observable enols.

β‐Keto Amides: A Jack‐of‐All‐Trades Building Block in Organic Chemistry

“… [69] The reaction of 90 with phenylisocyanate 87 (R = Ph) afforded α ‐sulfonyl β ‐keto amide 91 in 92 % yield (Scheme 16). [70] Mesoionic monosubstituted β ‐keto amide 93 could be synthesized by the reaction of pyridinium ylides 92 with phenylisocyanate in excellent yield (Scheme 16). [71] A solid‐phase synthesis of β ‐keto amides 98 by the reaction of immobilized isocyanate 95 , derived from Rink‐amide resin 94 , and lithium enolates 96 was developed by Romoff et al (Scheme 17).…”