Bimolecular hydrogen shift

An early example having potential commercial importance comes from tlie Trost laboratory s synthesis of vitamin D analogs (Scheme 6-23) [51], Their combination of vinyl bromide 129 and alkyne 130 to form triene 131 led to a concise and efficient synthesis of (-i-)-alphacalcidiol (134). In this reaction, vinyl bromide 129 participates in a bimolecular Heck reaction with alkyne 130 and the resulting alkenylpalladium intermediate 133 undergoes subsequent intramolecular Heck reaction with the pendant terminal alkene to provide 131. Under the reaction conditions, some of the desired product undergoes a [1,7]-hydrogen shift to yield 132. After thermal recycling of the minor component, a remarkable 76% yield of 131 was obtained. 

In addition to these bimolecular reactions, two unimolecular processes further enlarge the picture, namely, a 1,2-hydrogen shift (eq. 10) and a P-scission (eq. 11). Both reactions find their analogy in alkoxyl radical... 

Bimolecular surface reactions reactants adsorption, 29 111-112 with single reactant, 29 108-109 1,1 -Binaphthyl, dehydrocyclization, 28 318 Binary oxides, 32 119 Binding energy, 32 160-162 chemisorbed sulfur, 37 281 hydrogen, sulfur effect, 37 295-296 shift, Pd, 37 62-64 ZnO/SiOj, 37 21-22 Binor-S, see Norbomadiene Biological systems, hydrogen in, activation of, 11 301... 

Dehydrohalogenation of aliphatic and attcyctic chlorides. Brown2 noted that the bimolecular elimination of hydrogen halide from alkyl halides shifts to the Hofmann type by increasing the steric requirements of the base. Thus the elimination reaction... 

Catalase was found to form an intermediate compound in the presence of hydrogen peroxide (Chance, 69). The spectrum was measured from 380-430 nqi and is slightly shifted toward the visible as compared with free catalase. The complex shows no similarities to cyan-catalase or the compound formed when peroxide is added to azide catalase. Its formation is very rapid, the bimolecular velocity constant having a value of about 3 X 107 M.-1 sec.-1. In the absence of added hydrogen donors, the complex decomposes slowly according to a first order reaction with a velocity constant of about 0.02 sec.-1. This catalase complex thus resembles the green primary hydrogen peroxide complex of peroxidase. 

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