Catalyst Choice for Highly Enantioselective [3 + 3]​-​Cycloaddition of Enoldiazocarbonyl Compounds

By Marichev, Kostiantyn O.; Adly, Frady G.; Carranco, Alejandra M.; Garcia, Estevan C.; Arman, Hadi; Doyle, Michael P. From ACS Catalysis (2018), 8(11), 10392-10400.

Chiral copper(I) catalysts are preferred over chiral dirhodium(II) catalysts for [3 + 3]​-​cycloaddn. reactions of enoldiazocarbonyl compds. with nitrones and acyliminopyridinium ylides, forming chiral oxazines I (Z = Ph, Me, ibu, etc.; R1 = Ph, 2-​OMeC6H4, 4-​OMeC6H4; R2 = Ph, 2-​thienyl, 2-​furyl, etc.) and pyrazines II (Z = Ph, Me, ibu, etc.; Ar = Ph, 4-​OMeC6H4, 4-​BrC6H4, etc.) in very high yield and enantioselectivity.  Yields and stereoselectivities from reactions of enoldiazoketones are virtually the same as those from the corresponding esters and amides, but products from enoldiazoketones are precursors to chiral 1,​3-​dicarbonyl derivs. that provide addnl. opportunities in heterocyclic synthesis through the formation of pyrazoles and isoxazoles.