Asymmetric C(sp)-H Addition of Terminal Alkynes to Cyclopropenes by a Chiral Gadolinium Catalyst

We herein report the diastereo- and enantioselective C(sp)-H addition of terminal alkynes to cyclopropenes by a chiral half-sandwich gadolinium catalyst. This protocol constitutes the first example of asymmetric hydroalkynylation of cyclopropenes with terminal alkynes and offers a straightforward and 100% atom-efficient route for the synthesis of a wide range of enantioenriched alkynylcyclopropane derivatives in high yields (65-96%) and excellent stereoselectivity (>20:1 dr; 90-99% ee). Elaboration of some of the alkynylcyclopropane products through selective transformation of the C equivalent to C moiety has also been demonstrated to give further diversified chiral cyclopropane derivatives which are otherwise difficult to access.