Boronic cyclopropyl-substituted

The synthesis of medicinally relevant 4-substituted 2(5//)-furanones has been achieved by a coupling reaction of the triflate derived from p-tetronic acid with alkyl-and cyclopropylboronic acids (Scheme 10.8).22 This reaction was mediated by bis(acetonitrile)dichloropalladium and silver oxide. Interestingly, optically active cyclopropyl boronic acids were not racemized during this coupling reaction. 

A mixture of sodium borohydride and boron trifluoride-diethyl ether complex (each two equivalents) in tetrahydrofuran has been used for the reduction of cyclopropanone A,0-acetals to give A-(cyclopropyl)arylamines 2. This method was applied to various substituted A-aryl compounds. ... 

As is the case for cross-coupling reactions, arylstannanes and aryltriaUcoxysilanes can be substituted for boronic acids in this method, but would appear to offer few advantages. A number of other, usually Cu(II)-catalysed, reagents can be used to arylate azoles and indoles, of which diaryliodonium salts are the most useful. Aryllead triacetates and triarylbismuth diacetates may find very occasional use, but A-cyclopropylation using tricyclopropylbismuth with cupric acetate is possibly more interesting. ... 

The formation of homoallylpalladium intermediates of type 77 from the initial car-bopalladation products 76 can essentially be described as an intramolecular carbopallada-tion of one of the proximal cyclopropyl bonds by the adjacent cyclopropylpalladium moiety. Thus, the analogous silyl-substituted homoallylpalladium intermediates 85 also arise via intramolecular carbopaUadation, and this is not followed by /3-dehydropaUadation, but by reductive elimination to give the homoallylsilanes, -boronates, -stannanes, and so on 86—(Scheme 21). This type of overall transformation of bicyclopropylidene (50) is particularly versatile with trimethylsilyl cyanide, as it yields the trimethylsilyl-substi-tuted 4-cyclopropylidenebutyronitrile 86—CN that can readily be converted to a number... 

Palladium-catalyzed cross-coupling reaction of aryl-, alkenyl-, and cyclopropyl-boronic acids with 4-trifluoromethanesulfonyloxycoiunarin provides the corresponding 4-substituted coumarins in 63-85% yields (Equation 39) [39]. 

This q clopropyl boronic ester was converted into fois-cyclopropanes through a series of transformations shown in Scheme 3.79 [120], The iodo fois-cyclopropyl boronic acid ester 145, however gave a complex product mixture on attempted Suzuki coupling with phenylboronic acid. On the other hand, the less bulky hydroxy protected fois-cyclopropyldioxaborinane 146 obtained by transesterification underwent smooth cross-coupling with iodobenzene giving the phenyl substituted fois-cyclopropane product 147 in 79% yield (Scheme 3.79). 

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