RECENT PROGRESS IN THE ASYMMETRIC SYNTHESIS OF α-SUBSTITUTED PROPARGYLAMINES

Supported metals on porous solids as heterogeneous catalysts for the synthesis of propargylamines

This perspective summarizes recent developments in the synthesis of propargylamines using porous solids (zeolites, MOFs and carbon) as supports/catalysts.

Recent developments in asymmetric multicomponent reactions

Multicomponent reactions (MCRs) receive increasing attention because they address both diversity and complexity in organic synthesis. Thus, in principle diverse sets of relatively complex structures can be generated from simple starting materials in a single reaction step. The ever increasing need for optically pure compounds for pharmaceutical and agricultural applications as well as for catalysis promotes the development of asymmetric multicomponent reactions. In recent years, asymmetric multicomponent reactions have been applied to the total synthesis of various enantiopure natural products and commercial drugs, reducing the number of required reaction steps significantly. Although many developments in diastereoselective MCRs have been reported, the field of catalytic enantioselective MCRs has just started to blossom. This critical review describes developments in both diastereoselective and catalytic enantioselective multicomponent reactions since 2004. Significantly broadened scopes, new techniques, more environmentally benign methods and entirely novel MCRs reflect the increasingly inventive paths that synthetic chemist follow in this field. Until recently, enantioselective transition metal-catalyzed MCRs represented the majority of catalytic enantioselective MCRs. However, metal contamination is highly undesirable for drug synthesis. The emergence of organocatalysis greatly influences the quest for new asymmetric MCRs.

Asymmetric alpha-alkynylation of piperidine via N-sulfinyliminium salts

Piperidine was stereoselectively alpha-alkynylated in a four-step sequence made up of transformation to a chiral nonracemic N-sulfinylpiperidine, anodic oxidation to N-sulfinyliminium ion equivalent, alkynylation through addition of a mixed organoaluminum derivative, and final acidic deprotection of the sulfoxide. Overall yields are around 50%, and the diastereoselectivity of the nucleophilc addition was between 92 and 99% de, allowing isolation of the final product with 99% enantiomeric purity.

Direct addition of alkynes to imines and related CN electrophiles: A convenient access to propargylamines

Propargylic amines are highly useful building blocks in organic synthesis, and the corresponding structural motif has been found in various natural products and compounds of pharmaceutical relevance. This article provides an overview of the most significant advances in the preparation of propargylic amines via the direct addition of alkynes to imines and related carbon-nitrogen electrophiles in the presence of metal catalysts or promoters.