N-heterocyclic carbene catalysis: expansion of

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Title: N-heterocyclic carbene catalysis: expansion of
Author: Ogle, James William
Abstract: Asymmetric hydrogenation as a general route to polypropionates has been explored for allylic alcohols , acids , and derivatives , which has led to the generation of 2 ,4 -dimethylated hexane derivatives . Quantitative yields in most cases and enantioselectivities greater than 98 % were obtained . A remarkable stereofacial inversion was observed when an ester or acid was present in the allylic position instead of an alcohol or alcohol derivative . This led to the construction of all four diastereomers of the hexanol series from a single enantiomer of hydrogenation catalyst . Also described are an attempted synthesis of ( - ) -lardolure , a formal synthesis of the methyl ester portion of the preen gland extract from the domestic goose Anser anser , and a total synthesis of an extract from the fungi A . cruciatus . The synthesis of these compounds demonstrated shortcomings of the known catalyst system showing enantioselectivities for polymethylated compounds was high , while diastereoselectivity was low . Methodology to develop new N -heterocyclic carbene catalysts was developed using the cyanide coupling of aldimines to generate electronically tunable 1 ,3 ,4 ,5 -tetraaryl complexes , and X -ray , IR , and calculations were used to elucidate their electronic characteristics . These studies indicate that the 4 ,5 -positions have as great an influence on the metal -ligand bond as the 1 ,3 -positions . In addition , they are among the most electron -donating 2 - metalated N -heterocyclic carbenes found thus far . An intrinsic relationship between catalytic activity and electron donating ability was found in transfer hydrogenations .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3126
Date: 2009-05-15

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N-heterocyclic carbene catalysis: expansion of. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3126 .

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