Synthesis and reactivity of enantiomerically pure N-alkyl-2-alkenyl azetidinium salts

A synthesis of stereodefined enantiomerically pure 2-alkenyl azetidines is described using Wittig olefination as key step. The quaternary triflate ammonium salts of these heterocycles were prepared in a stereoselective way and treatment of these azetidinium salts with a base (KHMDS or PhLi) induced a regioselective Stevens rearrangement leading to a 3-alkenyl pyrrolidine. An unprecedented S_N2′ reaction involving phenyllithium as nucleophile and an ammonium as leaving group was observed in one case.     

Ynamides: Versatile Tools in Organic Synthesis

Ynamides display an exceptionally fine balance between stability and reactivity. They also offer unique and multiple opportunities for the inclusion of nitrogen‐based functionalities into organic molecules, and are emerging as especially useful and versatile building blocks for organic synthesis. Recent breakthroughs in the preparation of these substrates have revitalized interest in nitrogen‐substituted alkynes, and the beginning of the 21st century has witnessed an ever‐increasing number of publications reporting the development of new reactions or synthetic sequences starting from ynamides. This Review highlights major developments in this area.     

Total synthesis of chaetominine

An efficient, asymmetric synthesis of the cytotoxic natural product chaetominine was achieved in 14 steps. The strategy employs a copper(I)-mediated cyclization reaction as a key step to install the abc-tricyclic ring system, which was further elaborated by diastereoselective oxidation and reduction reactions. This effort also documents the first example of an oxidative rearrangement yielding to homochiral spirocyclic pyrrolidinyloxindoles.     

Copper-catalyzed oxidative alkynylation of diaryl imines with terminal alkynes: a facile synthesis of ynimines

An efficient copper-mediated method for the oxidative alkynylation of diaryl imines with terminal alkynes is reported. This reaction provides the first catalytic and general synthesis of ynimines and allows for an easy preparation of these useful building blocks. An improved copper-catalyzed oxidative dimerization of imines to azines and the synthesis of dienes and azadienes from ynimines are also described.     

Efficient and Divergent Synthesis of α‐Halogenated Amides and Esters by Double Electrophilic Activation of Ynamides

An efficient and modular entry to α‐halogenated amides and esters is reported. This reaction is based on an underestimated double electrophilic activation of ynamides sequentially involving highly reactive activated keteniminium and iminium ions. Upon simple reaction with HCl and an electrophilic halogenation reagent in the presence of water or an alcohol, a broad range of ynamides can be transformed, in a highly divergent manner, to α‐halo amides and esters with high efficiency and under mild conditions.     

Copper‐Mediated Coupling of 1,1‐Dibromo‐1‐alkenes with Nitrogen Nucleophiles: A General Method for the Synthesis of Ynamides

Mild reaction conditions are the advantage of the title reaction, which allows straightforward entry to a variety of ynamides starting from readily available 1,1‐dibromo‐1‐alkenes, which act as attractive alkynylating agents (see scheme; EWG=electron‐withdrawing group, DMF=N,N‐dimethylformamide).