New spiro derivatives of penicillin

The first example of carbenoid ring expansion of thiophene to a 2H-thiopyran has been observed in its Rh-catalysed reaction with benzhydryl 6-diazopenicillanate. Buchner ring expansion of anisole with the same carbenoid gives two isomeric methoxy-cycloheptatrienes by attack on the upper face of the β-lactam ring. In one of the isomers, the methoxyl group shows a strong conformational preference in solution, revealed by n.O.e. difference speotroscopy.