Concerted 6π electrocyclization of conjugated trienes is a well-known fundamental organic annulation process, which has been extensively studied since Woodward and Hoffmann formulated the principle of conservation of orbital symmetry, and these processes are widely employed in organic synthesis to construct new carbon-carbon bonds. Here we report a novel ruthenium-mediated cycloaromatization of conjugated trienes at ambient temperature with excellent yields (88 – 92%) within several hours. Kinetic studies of all three isomeric 1,2-di(prop-1-en-1-yl)cyclohex-1-ene substrates with ruthenium indicate that the rate-limiting cyclization step highly depends on the different observable intermediate structures. The first example of transition metal catalyzed 6π electrocyclization was observed when a more sterically hindered triene 1-(2-methylprop-1-en-1-yl)-2-(prop-1-en-1-yl)cyclohex-1-ene was employed as substrate at ambient temperature. The mechanisms of these annulation-aromatization processes were further investigated by deuterium labeling studies.

Transition metal-catalyzed cycloaromatization of conjugated trienes

2019 Fall National Meeting

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