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Although 18, in which an aziridine serves as surrogate for dehydrovaline gave 21 in low yield, the
formation of this penem lends circumstantial support to the Arnstein proposal for penicillin biosynthesis
involving a thioaldehyde. Ring strain in 20 and the propensity for the aziridine to undergo expansion is
probably responsible for the difference between our result and that of Scott.14
ACKNOWLEDGEMENTS
We are grateful to Professor Sigeru Torii, Okayama University, for helpful discussions and to the U.S.
National Science Foundation for financial support.
REFERENCES AND NOTES
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