Alkenes 1,2-bifunctionalized

Dienes. The bifunctionality of dienes makes their hydroboration more complex than that of simple alkenes. Competing hydroboration of the two double bonds may lead to mixtures of products arising from mono- or diaddition. Additionally, cyclic or polymeric organoboranes may be formed. Differences in the reactivity of the two double bonds and the use of appropriate hydroborating agents, however, may allow selective hydroboration.29,330... 

Various 1,2-bifunctionalized alkenes containing heteroatoms are prepared by addition to alkynes. Thiophosphorylation of 1-octyne with phosphorothiolate 131 provided (Z)-l-(diphenoxyphosphinyl)-2-(phenylthio)-l-octene in good yield [40]. A useful synthetic method for (Z)-3-phenylthioacrylate derivative is the Pd-catalyzed thioesterification of 1-alkynes with 6)-methyl S-phenyl thiocarbonate (132). Addition of 132 to 1-octyne using Pd(PCy3)2 as a catalyst afforded methyl (Z)-3-phenylthio-2-nonenoate in 86% yield [41]. (Z)-l,2-Bis(phenylthio)alkene was prepared in good yield by stereoselective Pd-catalyzed addition of (PhS)2 (3) to 1-alkyne [2]. 

Notably, catalysts with redox properties, such as molybdenum-, chromium-, and vanadia-based catalysts, show high activity in various oxidative dehydrogenation reactions of hydrocarbons [45 8]. Factors influencing the reaction also include acid-base bifunctionality, which plays an important role in CO2-mediated dehydrogenation reactions [49]. Both basic sites and Lewis-acid vacant sites are important for hydrocarbons activation [50]. In fact, an enhanced basicity results in an improved performance because of the rapid desorption of the electron-rich alkenes, whereas Lewis acid sites enhance the dehydrogenation process [51]. In addition, in the presence of CO2 as feed, surface basicity favors the adsorption and reactivity of the acid CO2 molecules [52] (see also previous chapters). 

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