6-Diazopenicillanates. Part 1. Reactions with furans
Abstract
Benzhydryl, p-nitrobenzyl, and pivaloyloxymethyl esters of 6-diazopencillanic acid undergo rhodium-catalysed reactions with furan giving 6-(4′-oxobut-2-enylidene)penicillanates in high yields. Substitution on the furan ring results in a strong steric effect at the 2-position and reveals the detrimental effects of electron-withdrawing groups at positions 2 and 3. The absence of a marked steric effect in 3-methylfuran indicates that the reaction does not involve initial, direct cyclopropanation, contrary to earlier claims. Addition of the 6-diazopenicillanate to benzofuran provides the first reported example of a carbenoid ring expansion of the latter.
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