Pinacol cross-coupling

The first asymmetric total synthesis of acosamine and daunosamine starting from a nonsugar precursor was reported by Fuganti and co-workers [288,289,290,291]. They found that baker s yeast catalyzes the asymmetric pinacolic cross-coupling of cinnamaldehyde and ethenal giving a ft-diol 156. This diol is protected as an acetonide and submitted to ozonolysis giving L-157. Olefination of L-157 with PhsP = CHCOOMe, followed by treatment with ammonia, provides 158 that is then converted into W-trifluoroacetylacosamine 158 (O Scheme 61). 

Olefin migration Oxidation of alcohols Passerini reaction Pauson-Khand reaction Pinacol cross-coupling Pinner reaction Polymerization of olefins Prins reaction Propargylation Radical addition Radical cyclization Radical substitution Reduction... 

In contrast to the above, N air et al. reported that f or the reaction between chalcones and aldehydes promoted by the In-InCl3 system, the pinacol cross-coupling product instead of p,y-unsaturated ketones was obtained [285] (Figure 8.129). 

Pinacol coupling. Yb(0) metal can effect pinacol reduction of aromatic, but not aliphatic ketones.1 However, it can effect cross-coupling of benzophenone with aliphatic ketones, often in high yield (equation I). 

Reduction of ketones other than 48 to dimers has been examined. Ethyl pyridyl ketone (51) gave a poor yield of the corresponding pinacol (52).79 Pinacols can also be made from crossed coupling of ketones with 3-(48).80 Finally, a study of the radical anions formed from the isomeric benzoylpyr-idines (53) was done, and the rates of rotation of the pyridyl ring were determined.81 The mechanism of reduction of the oxime and thiosemicar-bazone derivatives of 53 was determined by voltammetry techniques.82 The monoimine derivative of the pyridil 54 was reduced to the a-amino ketone 55 (Scheme 18).83 Unsaturated pyridyl ketones and heteroaryl pyridyl ketones have also been studied by voltammetry.84,85... 

Piezochromism, polysilanes, 3, 609 PIMS, see Photoionization mass spectrometry Pinacolboranes, cross-coupling reactions, 9, 170 Pinacolboronates, synthesis, 9, 167 Pinacol coupling... 

Indium mediated Barbier-type cross coupling between carbonyl compounds and allyl halides proceed efficiently under solvent-free conditions. No apparent competing pinacol-coupling or homo-coupling of the allyl halide was observed. The reactions were found to be mediated also by zinc, tin, bismut and copper [45]. 

The cross-coupling reaction of bis(pinacolato)diborane(4) [(Me4C202) B-B(02C2Me4)] with allyl acetates provided the pinacol esters of allyl-boronic acids with common structure 74 with regio- and fi-stereoselectively in high yields as 75-84 have been reported (Scheme 15). The reaction was efficiently catalyzed by Pd(dba)2 in DMSO at 50 °C.66... 

Synthesis of pinacol arylboronates 190 200 via cross-coupling reaction of bis(pinacolato)diborane(4) with chloroarenes catalyzed by palladium(O)-tricyclohexyl-phosphine complexes has been demonstrated by Ishiyama et al. (Scheme 31).115... 

Cross-coupling reactions of ArCOAr. Reaction of Yb(0) with diaryl ketones changes the reactivity of the carbonyl group from electrophilic to nucleophilic. Thus in the presence of this lanthanoid metal, diaryl ketones couple with other ketones, nitriles, and epoxides to give pinacols, a-hydroxy ketones, and 1,3-diols, respectively, via the intermediate a. 

The Suzuki-Miyaura tactic carried out on solid support (Scheme 28) [52] provides routes to small libraries of condensed heterocycles. Thus, Merrifield resin with the LeznofF-linked bromobenzene derivative 78 undergoes cross-coupling under normal solution-phase conditions with boron pinacolate 79 or boronic acid 80, prepared by DoM, to afford phenan-thridines 81 or, via 82 and some manipulation, dibenzopyranones 83 in good yields and with high purities. The Stille solid-support reaction has also been successfully executed [53]. 

Both amido and pinacol derivatives of B-Si compounds 125 and 126 added to terminal and internal alkynes in the presence of a palladium244-246 or platinum(O) catalyst247 by a mechanism involving an oxidative addition-insertion process (Equation (39)).248 On the other hand, phosphine-free nickel(O) catalyst resulted in the dimerization of alkynes giving a Z,Z-isomer of l-silyl-4-borylbutadiene derivatives.249 Since the palladium-catalyzed cross-coupling at the C-B bond is faster than the G-Si bond of 137, a silylboration-cross-coupling sequence provided a method for the synthesis of 1-alkenylsilanes.246... 

The total synthesis of the proteasome inhibitor cyclic peptide TMC-95A was accomplished by. S.J. Danishefsky and co-workers. The biaryl linkage in the natural product was constructed by a Suzuki cross-coupling between an aryl iodide and an arylboronic ester derived from L-tyrosine. The required arylboronic pinacolate substrate was prepared using the Miyaura boration. The aryl iodide was exposed to b/s(pinacolato)diboron in the presence of a palladium catalyst and potassium acetate in DMSO. The coupling proceeded in high yield and no symmetrical biaryl by-product was observed. 

Ishiyama, T., Ishida, K., Miyaura, N. Synthesis of pinacol arylboronates via cross-coupling reaction of bis(pinacolato)diboron with chloroarenes catalyzed by palladium(0)-tricyclohexylphosphine complexes. Tetrahedron 2001, 57, 9813-9816. 

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