Hydroboration-coupling protocol

Alkylboranes 103 are easily prepared by hydroboration of 1-alkenes with 9-BBN, and subsequent reactions with aryl, alkenyl, and alkyl halides offer versatile methods of dkylation to afford alkylated products 104, 105, and 106. The hydroboration-coupling protocol has been utilized extensively in natural product syntheses [87]. 

Some effected the coupling of phenyl-, 2-fuiyl-. and 1-hexenylboronic acids with 4-thallated indole-3-carboxaldehyde (Pd(OAc),/DMF) to give 4-substituted 3-formylin-doles [148]. Regioselective thallation of indole-3-carboxaldehyde is achieved using thallium tris-trifluoroacetate in 77% yield. Indole 129, which is available by the Buchwald zirconium indoline synthesis, was used by Buchwald to synthesize 130 via a Suzuki protocol [149]. Boronate ester 130 is prepared by the hydroboration of3-methyl-1-butyne with catechol borane. Indole 131 had been used in earlier studies to synthesize the clavicipitic acids. 

Palladium-catalyzed hydroboration, haloboration, and similar reactions involving addition of organoboron compounds to alkynes have been reviewed.Alkylborane addition to alkynes followed by intra- or intermolecular cross-coupling with a vinyl halide or triflates according to the Suzuki-Miyaura protocol constitutes a very powerful synthetic route for the generation of two carbon-carbon bonds in cascade. This subject and its applications in synthesis have been reviewed. ... 

Molander has recently reported the preparation of various 3-functionalized propyl trifluoroborates from the corresponding allyl derivatives following various literature protocols for hydroboration of alkenes [127]. The 3-heteropropyl trifluoroborates were obtained as crystalline air-stable solids by treatment of hydroboronated products with KHFj. Palladium-catalyzed cross-coupling of these 3-heteropropyl trifluoroborates with 4-acetylphenyl triflate gave functionalized alkylarenes in good yields (Scheme 3.82). 

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