Regio-and Stereoselective Synthesis Of Heteroatom-Substituted Olefins

Heteroatom-substituted olefins play a pivotal important role in organic chemistry, and consequently, the interest in these motifs has been long standing. However, the regio-and stereoselective formation of heteroatom-substituted alkenes remains to be explored. Herein, a couple of methods for accessing heteroatom-substituted alkenes have been realized, by the regio-and stereoselective addition of heteroatom-substituted alkynes. The work consists of three parts:Firstly, a Pd-catalyzed stereospecific trans-addition of boronic acids to ynamides has been achieved for the first time, furnishing (E)-α,β-disubstituted enamides in high yields with excellent regio-and stereoselectivity. It represents the first Pd-catalyzed trans-addition of boronic acids to alkynes so far. A possible mechanism involving the palladium carbene intermediate has been proposed to account for the unusual trans-addition.Then, a Pd-catalyzed cis-addition boronic acids to ynamides has been realized to provide (Z)-α,β-disubstituted enamides in excellent regio-and stereoselectivity. Clearly, it provides a complement method for the acess of stereodefined polysubstituted enamides.Finally, an iron-catalyzed regio-and stereoselective chlorosulfonylation of aromatic chloroalkynes has been achieved, giving cis-1,2-dichlorovinylsulfones in satisfactory yields with good to excellent stereoselectivity. It provides a new effective protocol for the synthesis of thermodynamically unfavorable cis-1,2-dichloroalkenes.