posted on 2005-02-18, 00:00authored byChien-Tien Chen, Jen-Huang Kuo, Vijay D. Pawar, Yogesh S. Munot, Shieu-Shien Weng, Cheng-Hsiu Ku, Cheng-Yuan Liu
Among six different group VIb oxometallic species examined, dioxomolybdenum dichloride and
oxomolybdenum tetrachloride were the most efficient catalysts to facilitate nucleophilic acyl
substitution (NAS) of anhydrides with a myriad array of alcohols, amines, and thiols in high yields
and high chemoselectivity. In contrast to the well-recognized redox chemical behaviors associated
with oxomolybdenum(VI) species, the catalytic NAS was unprecedented and tolerates virtually all
kinds of functional groups. By using benzoic anhydride as a mediator for in situ generation of an
incipient mixed anhydride−MoO2Cl2 adduct with a given functional alkanoic acid, one can achieve
oleate, dipeptide, diphenylmethyl, N-Fmoc-α-amino, pyruvic, and tert-butylthio ester, N-tert-butylamide, and trityl methacrylate syntheses with appropriate protic nucleophiles. The amphoteric
character of the MoO unit in oxomolybdenum chlorides was found to be responsible for the catalytic
NAS profile as supported by a control NAS reaction of using an authentic adduct−MoOCl2(O2CBut)2 between pivalic anhydride and MoO2Cl2 as the catalyst.