Lewis Acid Mediated Vinyl-Transfer Reaction of Alkynes to N-Alkylimines by Using the N-Alkyl Residue as a Sacrificial Hydrogen Donor

• Published in: Chemistry : a European journal 2013-10, Vol.19 (42), p.14263-14270
• Main Authors: Malakar, Chandi C., Stas, Sara, Herrebout, Wouter, Abbaspour Tehrani, Kourosch
• Format: Article
• Language: English
• Subjects: Additives; Alkynes; Alkynes - chemistry; amines; Amines - chemistry; Catalysis; Chemistry; Hydrogen - chemistry; Hydrogen storage; Imines; Imines - chemistry; Lewis acid; Lewis acids; Lewis Acids - chemistry; Mesylates - chemistry; Methodology; Models, Molecular; Molecular Structure; Propanols - chemistry; redox chemistry; Residues; Stereoisomerism; Terminals
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201300469

A variety of N‐alkyl‐α,α‐dichloroaldimines were vinylated by terminal acetylenes in the presence of Lewis acids such as In(OTf)3 or BF3⋅OEt2 and hexafluoroisopropanol (HFIP) as an additive. The reaction proceeds at ambient temperature and leads to geometrically pure allylic β,β‐dichloroamines. This approach is complementary to previously reported transition‐metal‐catalyzed vinyl‐transfer methods, which are not applicable to aliphatic imines and are restricted to imines that contain an electron‐withdrawing nitrogen substituent. In the present approach, terminal alkynes were used as a source of the vinyl residue, and the N‐alkyl moiety of the imine acts as a sacrificial hydrogen donor. The additional advantage of this methodology is the fact that no external toxic or hazardous reducing agents or molecular hydrogen has to be used. This new methodology nicely combines a C(sp2)C(sp) bond formation, hydride transfer, and an unusual cleavage of an unactivated CN bond, thereby giving rise to functionalized primary allylic amines. A detailed experimental study supported by DFT calculations of the mechanism has been done. Vinylation records: A variety of N‐alkyl‐α,α‐dichloroaldimines can be vinylated by terminal acetylenes in the presence of Lewis acids, such as In(OTf)3 or BF3⋅OEt2 and hexafluoroisopropanol (HFIP) as an additive. The reaction leads to geometrically pure allylic β,β‐dichloroamines (see scheme). Terminal alkynes were used as a source of vinyl residue, and the N‐alkyl moiety of the imine acts as a sacrificial hydrogen donor.