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DOI: 10.1055/sos-SD-024-01035

Witulski, B.; Alayrac, C.Science of Synthesis, (2006241031.

General Introduction

Electron-rich alk-1-yn-1-amines 1 have been known since the late 1960s, and since then their chemistry has been thoroughly investigated (see Section However, apart from a few examples,[‌1‌,‌2‌] their N-acyl and N-sulfonyl derivatives 2 were neglected, and the potential of the latter as building blocks in organic synthesis has only been recognized now that reliable and straightforward routes to them have become available.[‌3‌] With such methods in place, their chemistry has expanded tremendously,[‌4‌] as most of the drawbacks attributed to the chemistry of the parent alk-1-yn-1-amines, such as the lack of functionality at the nitrogen atom or their instability toward hydrolysis, can be overcome by the use of the corresponding sulfonamides 3, carboxamides, carbamates, and ureas 4, or cyclic variants, such as oxazolidin-2-ones 5 (X=O), imidazolidin-2-ones 5 (X=NR4), or pyrrolidin-2-ones 5 (X=CH2), as shown in Scheme 1.[‌4‌] Indeed, these compounds (often described as ynamides without further differentiation) are electron-deficient analogues of the alk-1-yn-1-amines, and the presence of the electron-withdrawing group decreases the ability of the nitrogen atom to delocalize its lone pair into the CC bond. As a result, the ketenimine contributor 6B is less important than the alk-1-yn-1-amine contributor 6A in the resonance description of such amides and sulfonamides, giving them greater stability than the corresponding parent alk-1-yn-1-amines (Scheme 1). Thus, ynamides are air-stable and withstand aqueous workup procedures; moreover, they are much easier to handle than their alk-1-yn-1-amine parents and can be purified by chromatography on silica gel.

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M8 M8 δ (M8) δ (M8) Mee
(MM8)8M(MM8)8 88 88 [‌88‌]
Me Me 88 88 [‌8‌]
Me Me 88 88 [‌8‌]
Me Me 88 88 [‌8‌]
88 88 [‌8‌]
Me Mee 88 88 [‌8‌]