Alkynyl N‐Nosylhydrazones: Easy Decomposition to Alknynl Diazomethanes and Application in Allene Synthesis

Abstract

The decomposition of N-tosylhydrazones is a safe and convenient method for the generation of donor carbenes. However, alkynyl carbenes cannot be isolated by this route because they readily undergo intramolecular cyclization to pyrazoles as soon as formed from alkynyl N-tosylhydrazones. Here, the use of alkynyl N-nosylhydrazones for the in situ generation of alkynyl carbenes and their coupling reaction with boronic acids under metal-free conditions is reported, giving rise to a wide array of di- and trisubstituted allenes. Preliminary mechanistic investigations demonstrated that γ-protodeboration of propargyl boric acid was responsible for the initial allene formation. This methodology based on the nosyl group allows for novel transformations that involve an alkynylcarbene transient species.

Luxury of N‐Tosylhydrazones in Transition‐Metal‐Free Transformations

“…[23] This resultw as in sharp contrast to the reactionw ith alkynyl N-tosylhydrazone which providedt he pyrazole under similar reactionc onditions.N otably, the side product of the reaction, alkyne 46,w as converted into the allene by stirring the crude reaction mixture with potassium hydroxide and tetra-n-butylammonium bromide( TBAB). [23] This resultw as in sharp contrast to the reactionw ith alkynyl N-tosylhydrazone which providedt he pyrazole under similar reactionc onditions.N otably, the side product of the reaction, alkyne 46,w as converted into the allene by stirring the crude reaction mixture with potassium hydroxide and tetra-n-butylammonium bromide( TBAB).…”

“…Although the whole discussion is centred on N ‐tosylhydrazones, it is worthy to note here the reactivity of N ‐nosylhydrazone which are able to decompose at room temperature to realize the in situ generation of carbenes. The coupling between alkynyl N ‐nosylhydrazones 44 and boronic acids under metal‐free conditions furnished the di‐ and trisubstituted allenes 45 (Scheme ) . This result was in sharp contrast to the reaction with alkynyl N ‐tosylhydrazone which provided the pyrazole under similar reaction conditions.…”

Transition-Metal-Free Reactions Between Boronic Acids and N-Sulfonylhydrazones or Diazo Compounds: Reductive Coupling Processes and Beyond

“…21 In this context, Bi, Zanoni et al reported the reaction of alkynyl N-nosylhydrazones with boronic acids, that led to the formation of allenes. 22 The reaction takes advantage of the ability of N-nosylhydrazones to undergo decomposition at lower temperatures than N-tosylhydrazones, preventing the intramolecular cyclization and allowing the intermolecular reaction with the boronic acid (Scheme 22). Under the optimized conditions the reaction features a remarkable scope, as both alkyl and arylboronic acids can participate in the coupling process.…”

“…The final treatment with KOH/TBAB isomerizes the alkyne 73 into the allene 72. According to the authors, 22 both protodeboronation pathways operate, representing an unprecedented example of γ-protodeboronation of propargylboronic derivatives (Scheme 24).…”

Research Progress on EWG-Substituted N-Arylsulfonylhydrazones as the Diazo Compound Precursor

“…然而, 炔基醛衍生的 N-对甲基苯磺酰腙在碱性 条件下, 很难通过分解的方法获得炔基卡宾化合物, 而 是发生分子内[3＋2]环合反应生成吡唑化合物 [24] . 2017 年, 我们课题组 [25] 6 Reactions of aromatic aldehyde derivated N-o-nitrophenylsulfonylhydrazones with α-diazo esters, amides and phosphonates 图 7 炔基醛衍生的 N-邻硝基苯磺酰腙与硼酸的反应 Figure 7 Reactions of alkynyl aldehyde derivated N-o-nitrophenylsulfonylhydrazones with boronic acids 随后, 我们课题组 [26] [17] , 采用氟代羰 基化合物衍生的 N-邻三氟甲基苯磺酰腙作为原料, 可 以在碱性条件下原位生成氟代重氮乙烷. 2019 年, 我们 课题组 [28] [33] .…”