An interesting issue of Diels-Alder selectivity discovered en route to 11-O-debenzoyltashironin.

The hypervalent iodine-mediated oxidative dearomatization/Diels-Alder cascade was examined in the context of the natural product 11-O-debenzoyltashironin. Interestingly, the regioselectivity of the Diels-Alder reaction can be completely switched by changing the dienophile. Trapping of allyl alcohols during the oxidative dearomatization gives rise to the five-membered acetal, while trapping of allenyl alcohols results in the six-membered acetal. [reaction: see text]