Preparation Of Multi-substituted Alkenylboronic Acids Via Carbomagnesiation And The Chlorination

Organoboronic acids are important nuclephiles which undergo Suzuki cross-coupling reaction and Petasis reaction. The synthesis methods of alkenylboronic acids are limited compared to the arylboronic acids. Many chemists focus their research interests on developling new methodologies to synthesize the stereodifined multi-substituted cis-alkenylboronic acid.Based on our previous work, we have focused on the synthesize of (Z)-2,2-disubstituted alkenylboronic acids from the propargyl alcohols by copper-catalyzed carbomagnesiation reaction and subsequent transmetalation reaction. Then the chlorination reaction of (Z)-2,2-disubstituted alkenylboronic acids with NCS was studied. The reaction temperature, reaction time, the equivalent of NCS and base are studied through the template reaction and an optimized condition was obtained, and the structure of the aimed product was identified by FT-IR, 1H NMR, 13C NMR and MS. The configuration of the product was confirmed to be maintained by two-dimensional 1H-1H NOESY spectrum. Several alkenylboronic acids with different function groups substituted were found to be suffered chlorination smoothly with moderate to high yield. As a result, we know that the trans-chloro alkene can be given by the chlorination reaction between (Z)-2,2-disubstituted alkenylboronic acids and NCS with high yield by mild reaction condition, and simple and convenient process.The carbomagnesiation of substituted propargyl alcohols with Grignard reagent was studied. The intermediate was trapped with D2O. Under the optimized condition, the deuterated allylic alcohol was got with good yield. Further more, the transmetallation reaction between the intermediate and boronic esters was researched. Unfortunately, 3,4-Disubstituted-1,2-oxaborol-2(5H)-ols were obtained and indentified in poor yields in this method. In regard to this, the steric effect the R group of substituted propargyl alcohols is proposed to hinder the transmetalation of intermediate with trialkyl borates.