Facial selectivity of the Ireland–Claisen rearrangement of allylic esters of 2-methyl and 2-methoxycyclopentanecarboxylic acids

Ketene silylacetals derived from prenyl and (Z)- and (E)-crotyl 2-methylcyclopentanecarboxylates () were subjected to the Ireland–Claisen rearrangement. All three substrates rearranged with complete facial selectivity, but the (Z)- and (E)-crotyl systems gave a mixture comprised of the same diastereomers of 1-(1-methyl-2-propenyl)-2-methylcyclopentanecarboxylic acid () in ratios of 2:1 and 1:2, respectively. In contrast, the ketene silylacetals prepared from allyl and prenyl 2-methoxycyclopentanecarboxylates () underwent rearrangements with both facial stereochemistries.