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

Chiral
copper­(I) catalysts are preferred over chiral dirhodium­(II)
catalysts for [3 + 3]-cycloaddition reactions of enoldiazocarbonyl
compounds with nitrones and acyliminopyridinium ylides, forming chiral
oxazines and pyrazines 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 derivatives that provide additional opportunities in
heterocyclic synthesis through the formation of pyrazoles and isoxazoles.