SUZUKI Selective Reduction

With a more complicated substrate 48, Suzuki et al. [34] removed the benzyl protecting group by use of calcium in ammonia, in which part of the diol product underwent partial saturation of the triple bond (Scheme 4.13). Hydrogenation of this mixture gave the fully saturated diol 49 in 87% yield. A thorough study was performed on selective reduction of benzyloxy alkyne 50 to give a mixture of hydroxy alkyne 51 and hydroxy trans-alkene 52 in 81-93% overall yields (Scheme 4.14) [12]. The study involved the use of different quantities of calcium and lithium in liquid ammonia. 

Suzuki-Miyaura cross-coupling polymerization of 1,4-bis((Z)-2-bromovinyl)benzenes with aryl-bis-boronic acids. The interest has been in an alternative approach, where rather than building a PPV with a pre-ordained stereochemistry, a postpolymerization yyn-selective reduction on a poly(phenylene ethynylene) (PPE) is used [125]. This scheme has the advantage that high molecular weight PPEs can be synthesized using either Pd-catalysis or alkyne metathesis. This route could also potentially allow for the access to an additional array of PPVs that are uniquely accessible from PPEs. The transformation of the triple bonds in PPEs and other acetylene building blocks to alkenes has considerable potential. 

Sonophotocatalysis is photocatalysis with ultrasonic irradiation or the simultaneous irradiation of ultrasound and light with photocatalyst. Tnis method includes irradiation with alternating ultrasound and light. Ultrasound effects on heterogeneous photocatalytic reaction systems have been demonstrated by Mason,1 Sawada et al.,2) Kado et al.,3) and Suzuki et al.4) In these papers, not only acceleration of photocatalytic reactions but increase in product selectivity by ultrasonic irradiation has also been reported. It was postulated that ultrasound effects, such as surface cleaning, particle size reduction and increased mass transfer, were the result of the mechanical effects of ultrasound.1,5) Lindley reviewed these and other effects.5)... 

For such a modular configuration, it is claimed that a large number of heterogeneously catalyzed reactions can be performed, e.g. Heck and Suzuki coupling, acid-catalyzed esterifications and reductions of functional groups [83], However, for the mentioned process, the catalyst and reactants are not named and no reaction conditions or experimental results, e.g. yield, selectivity or nature of side products, are given. 

Nevertheless, it must be pointed out that the formation of such transient species has never been spectroscopically observed. Native CDs are effective inverse phase-transfer catalysts for the deoxygenation of allylic alcohols, epoxydation,or oxidation " of olefins, reduction of a,/ -unsaturated acids,a-keto ester,conjugated dienes,or aryl alkyl ketones.Interestingly, chemically modified CDs like the partially 0-methylated CDs show a better catalytic activity than native CDs in numerous reactions such as the Wacker oxidation,hydrogenation of aldehydes,Suzuki cross-coupling reaction, hydroformylation, " or hydrocarboxylation of olefins. Methylated /3-CDs were also used successfully to perform substrate-selective reactions in a two-phase system. 

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