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11.10.5.4.1.2.1 Substitution with Formation of a C---C Bond

DOI: 10.1055/sos-SD-111-00323

Härtinger, S.Science of Synthesis Knowledge Updates, (20101149.

The Suzuki coupling of halo-substituted 1,2-benzisoxazole derivatives with an appropriately substituted arylborane reagent is accomplished in the presence of a palladium catalyst and a base, such as alkali or alkaline earth metal carbonates.[‌282‌-‌286‌] Suitable examples of borane reagents are phenylboronic acids, such as 222, and 4,4,5,5-tetramethyl-1,3,2-dioxaborolane derivatives thereof, e.g. 224 (Scheme 61). Representative palladium catalysts include tetrakis(triphenylphosphine)palladium(0), an analogous tolylphosphine complex [PdCl2(P-2-Tol3)2], and palladium catalysts with 1,1′-bis(diphenylphosphino)ferrocene ligands, such as dichloro[1,1′-bis(diphenylphosphino)ferrocene]palladium(II) [PdCl2(dppf)]. Microwave irradiation greatly reduces the reaction time.[‌286‌] The cross coupling between the benzisoxazole moiety and nonaromatic residues is more efficient with organotin compounds. The Stille reaction of vinylstannanes, such as 225, and iodobenzisoxazoles is achieved in the presence of bis(tri-tert-butylphosphine)palladium(0)[‌284‌] or dichlorobis(triphenylphosphine)palladium(II)[‌287‌] with cesium fluoride in refluxing toluene. In one isolated report, the alkylation of the aromatic ring has been accomplished with alkyllithium and Grignard reagents.[‌288‌] Careful optimization of the amount of organometallic reagents and reaction conditions is, however, required to suppress isoxazole ring opening. For the alkylation of 3-methyl-1,2-benzisoxazole (226), and substituted derivatives having methyl, methoxy, acetamido, and phenylsulfonamido groups, the deprotonation with lithium diisopropylamide in tetrahydrofuran at −78 °C in the presence of an iodoalkane is successful.[‌289‌,‌290‌]

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