Studies On The Functionalization Of Ynamides

Enamides and oxazolones occur in a number of natural products, and they are also important building blocks in organic chemistry. Thus, it is highly desirable to develop new effective access to assemble these motifs. In this paper, some synthetic useful methods have been developed for the synthesis of multisubstituted enamides and oxazolones featuring the functionalization reactions of ynamides. The whole work consists of five parts:Firstly, a Pd-catalyzed chloroallylation of ynamides is described, giving (E)-a-haloenamides in good yields and stereoselectivity. Moreover, the resultant products could be converted into tetrasubstituted enamides via the Suzuki coupling reaction.Secondly, a dichotomy method for the effecient synthesis of3,5-disubstituted and3,4,5-trisubstituted oxazolones has been realized by treating N-alkynyl tert-butyloxycarbamates with either Pd(CF3CO2)2or the combination of palladium catalyst, allyl halides, and Ag2CO3. The reaction is highlighted by the mild conditions, operationally simplicity, as well as high efficiency and selectivity.Thirdly, a Cu-catalyzed cyclization of N-alkynyl tert-butylcarbamates is presented. Compared with the Pd-catalyzed version, it provides a more practical alternative to3,5-disubstituted oxazolones due to the use of inexpensive Cu catalysts.Then, a Pd-catalyzed coupling of N-alkynyl fert-butyloxycarbamates with aryl halides has been developed, delivering3,4,5-trisubstituted oxazolones in good yields and with excellent diversity. Moreover, the resulting3,4,5-trisubstituted oxazolones are applicable to the construction of phenanthrene and naphthalene derivatives via a photochemical reaction.Finally, a Pd-catalyzed direct alkenylation of3,5-disubstituted oxazolones is reported. The use of alkenes, instead of haloalkenes, as the starting materials makes the reaction more atom-economic and effective entry to access3,4,5-trisubstituted oxazolones. Clearly, it further enlarges the scope of our methodology on the elaboration of polysubstituted oxazoleones.