Hiyama reaction mechanism

The MH-type reaction of silanols and organotin compounds with olefins via a Pd(II)-mediated pathway has been reported by Hiyama and co-workers. Based on this pathway, a plausible MH-type reaction mechanism with arylboronic acids was presented in Fig. 26. According to this mechanism, the aryl unit migrated to... 

Hiyama and Mori have reported that homo-coupling reactions of vinyl-, aryl-, and alkynylsilanes are effectively promoted by an equimolar amount of CuCl and air (Scheme 10.218) [565]. The reaction mechanism probably involves formation of organocopper species by Si-Cu transmetalation and subsequent oxidative dimerization by air. The strong tendency of CuCl to activate alkynylsilanes has been used for coupling reactions with 1-chloroalkynes (Scheme 10.218) [566]. 

SCHEME 19.49 Mechanism of the Hiyama reaction performed in the presence of nBu NR... 

The mechanism of the Hiyama aminoacrylate synthesis reaction is similar to the aldol condensation, as shown in Scheme 3.10. 

Carbostannylation sometimes proceeds with no activators, but the applicability of such reactions is severely limited to a few types of special substrates. The development of activation methods in the mid 1990s made carbostannylation a synthetically significant tool. Three major activators are now available. Thus, radical initiators, Lewis acids, and late transition metals were found to be effective as activators by Hosomi, Yamamoto, and Shirakawa-Hiyama, respectively. These activators are required only in a catalytic amount to promote the reaction. Scheme 5.7.2 summarizes the mechanism of the activation of carbon-tin bonds by these activators. The cleavage of carbon-tin bonds by a radical initiator gives a stannyl radical, which adds to an unsaturated bond. The resulting alkenyl or alkyl radical abstracts an R... 

Lewis acid breaks up the closed transition state normally found in thermal reactions. Contrary to the Hiyama-Nozaki reaction the induced stereoselections for allylstannanes-i-Lewis acids are extremely high, due to chelate-Cram controlled mechanisms [reaction (91), Scheme 30] [76]. Reagent controlled diastereoselec-tivity may be exerted in terms of 1,3- [reaction (92)] [77] and 1,5-inductions [reaction (93)] [78]. 

Various epimerases acting on carbohydrate derivatives and acyl-CoA derivatives were demonstrated, purified, and characterized as reviewed previously1184. Lactate race-mase (E.C. 5.1.2.1) is the first racemase to he discovered (1 41. The mechanism of lactate racemase reaction was studied with the enzyme preparations partially purified from Clostridium butyricumll8S. Hiyama et al.[1861 highly purified the enzyme from Lactobacillus sake, but little is known about its enzymological properties. In contrast, mandelate racemase (E. C. 5.1.2.2) is the enzyme best characterized among various racemases and epimerases its tertiary structure and functional groups that participate directly in catalysis has been clarified. 

Sonoike K, Hamo M, Hihara Y, Hiyama T and Enami I (1997) The mechanism ofthe degradation ofpsaB gene products, one of the photosynthetic reaction center subunits ofPhotosystem I, upon photoinhibition. Photosynth Res 53 55-63 Takahashi M and Asada K (1988) Superoxide production in the aprotic interior of chloroplast thylakoids. Arch Biochem Biophys 267 714-722... 

Although it has been reported that this reaction involves a radical intermediate, nonradical mechanisms are proposed here, including a stoichiometric Nozaki-Hiyama-Kishi reaction in Scheme 1, and a catalytic version of such reaction in the presence of manganese and trimethylchlorosilane in Scheme 2. 

SCHEME 1. Mechanism of regular Nozaki-Hiyama-Kishi reaction. 

SCHEME 2. Mechanism of Nozaki-Hiyama-Kishi reaction with manganese and TMSCI present. 

Scheme 1.14 (a) General conditions for the Hiyama-Hatanaka cross-coupling reaction, (b) The proposed mechanism for the Hiyama-Hatanaka cross-coupling arylation procedure [31]. 

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