Alkyne enantioselective

The enantioselective alkyne-imine addition has been achieved using a copper(i)-bis(oxazoline) compound in [G4GiIm]N(GF3S02)2 (Scheme 46). ... 

Jiang has subsequently reported the use of amino alcohol 319 in Zn-cata-lyzed enantioselective alkyne additions to aldehydes [192]. In an important development of the method, the substrate scope was expanded also to include non-enolizable a-ketoesters, such as 318 (Equation 22) [193]. 

An unprecedented nickel-catalyzed reductive coupling between an epoxide and an alkyne to give synthetically useful homoallylic alcohols has been developed by Jamison [55a], and was recently used in a short enantioselective synthesis of am-... 

The synthesis of 10 features the SN2 displacement of the allylic acetate with migration of R2 from the ate complex6. Precursors 9 are prepared by the hydroboration of 3-acetoxy-l-alkynes that are available with very high enantiomeric purity via the asymmetric reduction of the corresponding l-alkyn-3-ones, and a substantial degree of asymmetric induction occurs in the conversion of 9 to 10. Best results, based on the enantioselectivity of reactions of 10 with aldehydes, are obtained when R2 is a bulky group such as isopinocampheyl (79 85 % ee)6. The yields of reactions of 10 with aldehydes are 62-76%. 

In 2002, Braga el al. employed a chiral C2-symmetric oxazolidine disulfide as a ligand for the enantioselective synthesis of propargylic alcohols by direct addition of alkynes to aldehydes (Scheme 3.64). Good yields but moderate enantioselectivities (<58% ee) were obtained for the enantioselective alkyny-lation of aldehydes in the presence of ZnEt2. 

A number of chiral monodentate phosphines have been examined in asymmetric nickel-catalyzed reductive couplings of aldehydes and alkynes. The best results to date have been obtained with (+)-NMDPP (16) [33]. Aromatic internal alkynes and branched aldehydes participate with excellent enantiose-lectivity (Scheme 15), although yields and enantioselectivities were somewhat lower with other combinations of aldehydes and alkynes. In a complemen-... 

Scheme 4.38. Enantioselective formation of [Mactams from nitrones and alkynes.

Several Pd-catalyzed domino processes start with a Tsuji-Trost reaction, a pal-ladation of alkynes or allenes [5], a carbonylation [6], an amination [7] or a Pd(II)-cat-alyzed Wacker-type reaction [8]. A novel illustrious example of this procedure is the efficient enantioselective synthesis of vitamin E [9]. 

It has also been found that the indolizinoquinoline iV-oxidc 291 can be used as a chiral promoter in enantioselective Pauson-Khand reactions in the reaction of norbornene with various alkynes, ee s of up to 33% were obtained in the presence of this promoter <1998H(48)1445>. 

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