| 摘要 |
A process for preparing a beta -lactam compound of the formula (I): <IMAGE> (I) which comprises cyclization, in the presence of a catalyst, of an azetidinone derivative of the formula: <IMAGE> (II) is provided in which R1 is hydrogen, alkyl which is optionally substituted, or amino which is optionally substituted; R2 is a carboxy-protecting group; and X is alkylene which is optionally intervened by -O- or -S-, and/or which is optionally substituted; and R3 is aryl which is optionally substituted. The catalyst is preferably a transition metal salt (especially rhodium) or is an acid.
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