Synthesis reaction with boron reagents

In the initial discovery of the asymmetric synthesis of a-chloro boronic esters 3, the diastereomeric ratios of 3 were estimated by reaction with Grignard reagents to form secondary alkyl boronic esters 5 and deboronation with hydrogen peroxide to secondary alcohols of known absolute configuration and rotation40. 

Some articles have described synthesis of 3-trifluoromethylquinoline (271) [161-165]. Catalytic oxidative trifluoromethylation of 3-qunolineboronic acid (270) resulted in 3-trifluoromethylquinoline in 49 % yield [161]. Use Togni s reagent (272) in reaction with boronic acids 270 resulted in increase yield of 271 up to 53 % [162]. 3-Trifluoromethylquinoline was also obtained by reaction of boronic acids 270 with CF3I [163] or with trifluoromethyl sulfonium salts [164] in 87 % yield. Interaction of 3-iodoquinoline (273) with sodium trifluoromethyl formate at presence Cu and AgjO also led to compound 271 [165] (Scheme 80). 

Another reagent system that has been recently employed in the Paal synthesis of thiophenes is the combination of bis(trialkyltin)- or bis(triaryltin) sulfides with boron trichloride. Known as the Steliou reagent,it has been utilized in the transformation of 1,4-diketone 11 to thiophene 12. Higher yields are obtained in shorter reaction times in contrast to the use of Lawesson s reagent. Additionally, others have noted the relative ease of the work-up procedure using the Steliou conditions, and the fact that the tributyltinchloride byproduct of the reaction is reusable. Similarly, the combination of the bis(trimethylsilyl)sulfide has been used in conjunction with trimethylsilyltriflate for the preparation of thiophenes in an analogous manner. ... 

The use of expensive and unstable ZnPli2 in the preparation of chiral di-arylmethanol derivatives, with electronically and sterically similar aryl rings, made this approach less attractive for the enantioselective synthesis. In order to avoid this inconvenience, other alternative preparations of arylzinc reagents were evaluated.As a first choice, Yus et al. proposed the use of arylboronic adds as a viable source of phenyl (Scheme 4.19). Thus, the reaction of various boronic acids with an excess of ZnEt2 at 70 °C gave the corresponding arylzinc intermediates (probably aryl(ethyl)zincs), which were trapped by reaction with dif-... 

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