Direct Asymmetric α‐Sulfamidation of α‐Branched Aldehydes: A Novel Approach to Enamine Catalysis

Abstract

Proline‐catalysed reactions between α‐branched aldehydes and sulfonyl azides provide scalemic configurationally stabilised α‐sulfamidated products with ee values of up to 86 %. The reactions can also be carried out in a one‐pot fashion, with catalyst, aldehyde, sulfonyl chloride and sodium azide. The proposed mechanism differs fundamentally from the mechanistic model usually ascribed to enamine catalysis, containing as a key step the diastereoselective cycloaddition of the azide to an enamine formed in situ. The products obtained in the reaction can be converted into the corresponding unnatural amino acids in two additional steps.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Synthesis and Characterization of Carboxylic Acids Bearing Poly(ethylene glycol) Chains

“…As for oxidation of 6a to 1a, Jones oxidation conditions considerably cleaved the PEG chains of 6a. After several trials, 1a was successfully obtained in a two-step reaction: Swern oxidation, 8 which afforded 7a, and Pinnick oxidation, 9 which afforded 1a, in a high total yield (63% yield from 3). 10 With regard to 1b bearing three longer PEG chains (n = ca.…”

o-Nitrobenzenesulfonyl Azide

“…General conditions for the organocatalytic αsulfonylation of aldehydes were described. 26 The use of l-proline as a chiral organopromoter delivers the α-sulfonamide with moderate to high stereoselectivity. For example, a 4-methoxysubstituted hydratopaldehyde performed well under the optimized conditions, furnishing the desired sulfonamide in 53% yield and with 86% ee (eq 14).…”

Proline Sulfonamide Based Organocatalysis: Better Late than Never

“…In addition, there were several examples of transformations in which other catalysts such as the proline tetrazole 18 xx,xxxviii or proline itselfxxvii,xxxix,xl,xli prove superior. It became clear to us that while preliminary work demonstrated the viability of proline sulfonamides as organcatalysts, the unique reactivity of these catalysts had not been fully realized.…”