Hydroboration allylic alkenes, functionalized

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). 

Catalyzed hydroboration has proven to be valuable in controlling the stereoselectivity of hydroboration of functionalized alkenes.169 For example, allylic alcohols... 

By heating 32 in aqueous dimethyl sulfoxide (DMSO), containing sodium chloride, up to 170°C, loss of a methoxycarbonyl group and then -elimination of acetic acid occur to give alkene 33 in 70% yield. From this, carba-pl-L-mannopyranose 34 has been produced by conversion of the ester group to the hydroxymethyl function, hydroboration, and de-O-protection. Thus, the hydroboration step proceeded by cis-addition anti- to the allylic benzyloxy group. 

Functionalized alkenes and alkynes can be hydroborated . Directive effects are discussed in 5.3.2.5.1(i). As follows from Table 2, hydroboration of vinylic and allylic derivatives leads to the placement of boron in the a., fi or y position to the substituent. The -substituted organoboranes are prone to uncatalyzed cis elimination and acid- or base-catalyzed trans- elimination The rate of elimination depends on the substituent at... 

Borabicyclo[3.3.1]nonane (9-BBN) has found use in the selective hydro-boration of alkenes in the presence of other reducible functional groups and its reaction with alkynylstannates has been studied. o-Stannyl- and a-silyl-substituted crotyl-9-BBN show promise as reagents for the stereo-regulated synthesis of acyclic systems. A series of papers covers the question of olefin-alkyl exchange in. 5-alkyl-9-BBN s, " the kinetics of reduction of substituted benzaldehydes with 9-BBN, and the kinetics and mechanism of hydroboration of alkynes with 9-BBN dimers. Selective dehalogenation of tertiary alkyl, benzyl, and allyl halides in the presence of secondary or primary alkyl or aryl halides is possible with (165). The... 

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