Asymmetric synthesis of (R)-ar-curcumene, (R)-4,7-dimethyl-l-tetralone, and their enantiomers via cobalt-catalyzed asymmetric Kumada cross-coupling

An efficient and concise asymmetric synthesis of (R)-(+)-ar-curcumene, (R)-4,7-dimethyl-l-tetralone, and their enantiomers was accomplished. The key step to construct the stereogenic benzylmethyl centers of these natural products is the cobalt-catalyzed asymmetric Kumada cross-coupling reaction of a racemic α-bromo ester.

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(R)-1-Methyl-4-(6-methylhept-5-en-2-yl)benzene [(R)-ar-curcumene]C15H22Ee = 90%[α]D20 = −44.6 (c 1.2, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (R)

(R)-4,7-Dimethyl-3,4-dihydronaphthalen-1(2H)-oneC12H14OEe = 90%[α]D20 = +12.8 (c 1.3, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (R)