Regioselective and Enantioselective Nitrone Cycloadditions to Alkynones.
Abstract
There has been a need in agriculture, medicine, and organic chemistry for enantiopure
isoxazolines. A direct method for their synthesis is from the cycloaddition of 1,3-dipoles
and alkynes. Alkynones are difficult substrates to use in cycloadditions due to their high
reactivity and sometimes instability. Due to their high reactivity it is often difficult to
control regio- endo/exo, and enantioselectivities in dipolar cycloadditions of alkynones.
This thesis details the cycloadditions of nitrones and alkynones using chiral Lewis acids
leading to isoxazolines with high regio-and enantiocontrol. A chiral bisoxazoline-zinc(II)
complex successfully catalyzed the enantioselective 1,3-dipolar cycloaddition reaction of
nitrone and alkynone derivatives. This is the second successful reported method for the
catalytic enantioselective 1,3- dipolar cycloaddition of nitrones and alkynone derivatives.
Yields for the cycloadducts were good to near quantitative and enantioselectivities were
generally good reaching a high of 86 % ee. The 4-isoxazolines were isolated as single
reg101somers.