Boron compounds biaryl synthesis

Fuostifoline (47), a furo[3,2-a]carbazole, was isolated from Murraya euchrestifolia. Timdri s total synthesis of 47 commenced with alkylation of bromocresol 43 with bromoacetaldehyde diethyl acetal and P4Oio-promoted cyclization to furnish 5-bromo-7-methylbenzofuran (44) [47]. The Suzuki coupling of boronic acid 45, derived from 44, with o-bromonitrobenzene yielded biaryl 46. Nitrene generation, achieved via deoxygenation of nitro compound 46 using triethyl phosphite, was followed by cyclization to fuostifoline (47). 

Scheme 17 illustrates another fluorous sulfonate-based synthesis of library scaffolds. The tagged substrates were taken through aldol condensation and cycloaddition reactions to form the pyrimidine ring 18. The intermediates were then reacted with boronic acids for Suzuki reactions to form biaryl compounds 19 [31], reacted with HCO2H to give traceless detagged products 20 [34], or reacted with amine to form products 21 [33]. 

A recent example of the application of solid phase Suzuki reactions to the synthesis of pharmaceutically important biaryl compounds was shown by Nielsen et aL [115]. A range of aryl-substituted pyrroloisoquinolines were synthesized from biarylalanine precursors in high purity (Scheme 39). This involved a Suzuki coupling of sohd-supported iodophenylalanine derivatives containing a masked aldehyde to various boronic acids, followed by hberation of the aldehyde, TFA-mediated intramolecular Pictet-Spengler reaction, and cleavage. 

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