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Yang et al. Chem Synth 2023;3:7 https://dx.doi.org/10.20517/cs.2022.38 Page 7 of 54
Scheme 5. Asymmetric catalytic cascade reactions of benzolactone-derived olefins 1 and α, β-unsaturated ketones 9. This figure is used
with permission from the Royal Society of Chemistry [37] .
It is believed that the enantioselectivity was determined by the first Michael addition. While the Michal
addition of I to the chromone core via hydrogen bonds stabilized intermediate followed by an
intramolecular Henry cycloaddition was believed to be the substrate/catalyst-controlled diastereoselective
process. All the final products were successfully isolated and characterized in up to 76% yield with > 20:1 dr
and 98% ee.
Recently, Li et al. developed a highly enantioselective Diels-Alder reaction of benzolactone-derived olefins
[48]
1 with polyenals 15 catalyzed by diphenylprolinolsilyl ether C6 through a trienamine activation strategy,
which enabled diversity-oriented synthesis of a series of potentially bioactive multifunctional chiral
spirocyclohexenebenzolactone scaffolds 16 with moderate diastereoselectivities and good
enantioselectivities. It was demonstrated that this activation strategy lies within the perfect chirality relay
over a distance of up to eight bonds by combining trienamine catalysis with enamine activation
[Scheme 8A].
To further check the generality of the described work, late-stage chemical modification of the Diels-Alder
adduct 16a was examined. As shown in Scheme 8B, adduct 16a could be efficiently converted to highly
complex scaffolds 17a and 18a with good efficiency [Scheme 8B].
