On the stereoselectivities of some hindered Diels–Alder reactions

The cis-fused lactones were the major products isolated from Diels–Alder reactions of (2E,4E)-2,4-dimethylhexa-2,4-dienyl methyl fumarate and maleate and from the cyclisation of the all (E)-2,4,6,8-tetramethyldeca-2,4,6,8-tetraenyl methyl fumarate in contrast to the Diels–Alder reactions of analogous substrates that lack the dienyl 2-methyl group. All of these Diels–Alder reactions led to the introduction of a methyl bearing quaternary centre. An intramolecular Diels–Alder reaction of a 3-(5,7-dimethylnona-5,7-dienoyl)pyrrolinone also gave mainly the endo-product, in this case with two adjacent quaternary centres.

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