Solid-Phase Synthesis of Amino Acid Derived N-Unsubstituted Pyrazoles via Sydnones

Abstract

A new method to synthesize N-unsubstituted pyrazoles on a solid support is described. The solid support acts as a protecting group for the amino acid. N-Protected amino acid is N-nitrosated, and the subsequent treatment with acetic anhydride in a microwave reactor yields mesoionic sydnones that react in situ in 1,3-dipolar cycloaddition reactions with alkynes. Traceless cleavage of the products gives N-unsubstituted pyrazoles in high overall yields.

Cu‐Promoted Sydnone Cycloadditions of Alkynes: Scope and Mechanism Studies

“…The products were then easily isolated after cleavage from the solid support. [6] We have previously described examples of cycloaddition reactions of sydnones with alkynylboronate and found these to offer excellent regioselectivities towards the 3-substituted-4boronate pyrazole, [7,8] although regioselectivity is highly substituent-dependent under thermal conditions. This is a useful method for the generation of polysubstituted pyrazoles, since sydnones can be functionalized through cross-coupling reactions at the C4-position.…”

Physiological, Biochemical and Molecular Genetic Aspects of Heartwood Formation Mechanisms

“…Среди экстрактивных веществ основную массу составляют стильбены и смоляные кислоты. Отдельные деревья сосны существенно различаются между собой по количеству стильбенов в ядровой древесине, при этом указанный признак может передаваться от родителей потомству [Harju, Venäläinen, 2006;Harju et al, 2009;Partanen et al, 2011]. Помимо прямой фунгицидной активности стильбены обладают антиоксидантными свойствами, тем самым защищая растение от свободных радикалов, используемых многими грибковыми патогенами для разрушения клеточных стенок растения .…”

Recent Advances in Solid‐Phase 1,3‐Dipolar Cycloaddition Reactions

“…30 Sydnones are mesoionic compounds that react as azomethine imine-type 1,3-dipoles in 1,3-dipolar cycloaddition. 30 Sydnones are mesoionic compounds that react as azomethine imine-type 1,3-dipoles in 1,3-dipolar cycloaddition.…”