(3S,4S)-4-[(4S)-2,2-dimethyl-1,3-dioxolan-4-yl]-3-hydroxy-3-[(1S)-1-hydroxyprop-2-enyl]-1-(4-methoxyphenyl)azetidin-2-one 、
2,2-二甲氧基丙烷 在
4-甲基苯磺酸吡啶 作用下,
以90%的产率得到(1S,4S,8S)-1-[(4S)-2,2-dimethyl-1,3-dioxolan-4-yl]-8-ethenyl-2-(4-methoxyphenyl)-6,6-dimethyl-5,7-dioxa-2-azaspiro[3.4]octan-3-one