Nonfused, alkynyl-β-lactams 10 and 18 react with n-Bu3SnH to give tert-butyl carbaceph-2-em-4-carboxylate (11) and methyl 1-oxahomoceph-3-em-5-carboxylate (19), respectively, in a four-step, sequential radical reaction involving homolytic intermolecular addition, intramolecular hydrogen atom transfer, endo-intramolecular addition, and β-elimination.
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Bosch et al. (1993) studied this question.