Hydroboration regioselective

Clark and coworkers utilized enyne RCM for constructing the AB ring fragment of the manzamine alkaloids (Scheme 83) [177]. Exposing metathesis precursor 423 and ethylene gas to catalyst A provided bicycle 424 in near quantitative yield. Regioselective hydroboration of the vinyl group in 424, followed... 

A few functional group transformations were necessary to set the stage for the Koevenagel condensation of the p-keto ester 220 (Scheme 33). Ketone 215 was protected as a 1,3-dioxolane. Regioselective hydroboration of the terminal exocyclic double bond was then accomplished with 9-BBN and... 

Ellman used silyl chemistry for the direct linkage of aromatics onto the solid support by converting an aryl bromide to aryl lithium and reacting this with a silyl resin.90 It is the production of the silyl resin that is of interest in the context of this review, since an in situ Suzuki coupling was used to link the allyl silane to bromomethyl polystyrene resin (Scheme 40). 9-BBN is used to carry out the regioselective hydroboration, and this is linked to the resin with palladium catalysis in the usual way. After brief exposure of this... 

Step 1 Regioselective hydroboration of the terminal alkyne carbon. Step 2 Suzuki coupling. 

Hydroboration. This borane is recommended for hydroboration of alkynes, particularly for regioselective hydroboration of unsymmetrical alkynes (equation I). 1 -Alkynes are converted into aldehydes in high yield. Since alkenes react only slowly with this borane, selective hydroboration of alkynes in the presence of alkenes is possible. 

BH3 (regioselective hydroboration) then H202/H0" (H and OH are added in a syn- manner). 

Preparations. Functionalized organozinc reagents have been prepared from alkenes via stereoselective and regioselective hydroboration and B-Zn exchange. An interesting synthesis of carboxylic acids by chain extension from (o)-l)-unsaturated acids involves prior attachment to a resin (in the form of polymeric esters). ... 

Chloroborane (CIBH2) is a more regioselective hydroborating agent than borane (42). This property can be attributed to the heightened hardness of the boron atom. 

Hydroboration occurs with anti-Markovnikov regioselectivity Hydroboration-oxidation is syn stereoselective, with the H adding to the carbon with the fewer number of hydrogens. 

Scheme 15.34 Ligand-controlled regioselective hydroboration of terminal alkynes.

Catalytic hydroboration of terminal allg nes with B2(pin)2 is achieved by employing a copper catalyst. Products are obtained regioselectively by employing a suitable NHC ligand (Scheme 15.34). A bull bidentate phosphine ligand is effective for regioselective hydroboration of aryl-substituted... 

Scheme 15.35 Copper-catalysed regioselective hydroboration of uns5mimetrical...

---