Activated dehydrogenative coupling reactions

Stereoselective cross-dehydrogenative coupling reactions based on sp C—H activation to give chiral heterocycHc compounds 12JHC721. Suzuki—Miyaura cross-coupHng in acylation reactions, scope and recent developments 13MOL1188. 

It was reported that iron salts catalyzed the oxidative a-phosphonation of A,A-dimethylanilines with (R0)2P(0)H in the presence of tert-butylhydroperoxide [196]. In the study electrochemical C-H bond activation was utilized to generate iminium species, followed by C-P bond formation. An efficient dehydrogenative coupling reaction involving iminium salt as a possible intermediate was also reported with copper salt as catalyst and molecular oxygen as oxidant [197]. 

A number of compounds react rapidly with DDQ at room temperature. They include allylic and benzylic alcohols, which can thus be selectively oxidized, and enols and phenols, which undergo coupling reactions or dehydrogenation, depending on their structure. Rapid reaction with DDQ is also often observed in compounds containing activated tertiary hydrogen atoms. The workup described here can be used in all these cases. 

Dehydrogenative Coupling. Transition-metal catalyzed polymerization of silanes appears to hold promise as a viable route to polysilanes. A number of transition-metal complexes have been investigated, with titanium and zirconium complexes being the most promising (105—108). Only primary silanes are active toward polymerization, and molecular weights are rather low. The dehydrogenative polymerization is depicted in reaction 11, where Cp = cyclopentadienyl ... 

A single enzyme is sometimes capable of many various oxidations. In the presence of NADH (reduced nicotinamide adenine dinucleotide), cyclohexanone oxygenase from Acinetobacter NCIB9871 converts aldehydes into acids, formates of alcohols, and alcohols ketones into esters (Baeyer-Villiger reaction), phenylboronic acids into phenols sulfides into optically active sulfoxides and selenides into selenoxides [1034], Horse liver alcohol dehydrogenase oxidizes primary alcohols to acids (esters) [1035] and secondary alcohols to ketones [1036]. Horseradish peroxidase accomplishes the dehydrogenative coupling [1037] and oxidation of phenols to quinones [1038]. Mushroom polyphenol oxidase hydroxylates phenols and oxidizes them to quinones [1039]. 

Copper Catalysts Direct oxidative functionalization of tertiary amines is of importance both enzymatically and synthetically. The combination of CuBr—TBHP has proved to be as an efficient system in the oxidative activation of sp3 C—H bonds adjacent to a nitrogen atom [10]. Various types of cross-dehydrogenative coupling (CDC) reactions have been developed, including compounds with activated methylene groups [11], indoles [12], and terminal alkynes (Scheme 11.2) [13]. Because 1,2,3,4-tetrahydroisoquinoline derivatives are important structure motifs of natural... 

A. Coupling reaction using ferric chloride (FeCl ) as oxidant 1, The polymerization from homo-monomer Compound 16 isolated from Vitis amurensis showed strong biological activity [7, 65] and its biomimetic synthesis was achieved as shown in Fig. (7). Oxidative coupling reaction of 1 with FeCU as oxidant produced an intermediate, ( )- -viniferin (107), by silica gel column chromatography. After acetylation, it was dehydrogenated by treatment with 2,3-dichloro-5,6- dicyano-1, 4-benzoquinone (DDQ) to afford an intermediate(108) and the desired compound 16 in 20% yield [7]. 

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