Substrate-controlled diastereoselectivities in catalyzed and uncatalyzed hydroborations of acyclic allylic alcohol derivatives: secondary orbital effects involving d.pi.-p.pi. interactions

Calcium-mediated hydroboration of alkenes: “Trojan horse” or “true” catalysis?

“…1 (m, AA 0 XX 0 spin system, 2H), 6.38 (m, AA 0 XX 0 spin system, 2H), 6.65 (m, AA 0 XX 0 spin system, 2H), 6.71 (m, AA 0 XX 0 spin system, 2H). 11 B NMR (160 MHz, THF-d 8 , 25 C): d ¼ 9.2 ppm (sharp). The signal for the major species was assigned to the B(cat) 2 À ion.…”

Metal‐Catalyzed Cross‐Coupling Reactions of Organoboron Compounds with Organic Halides

“…Thus, the catalyzed reaction is more sensitive to steric effects than to electronic effects, whereas 9-BBN prefers to attack from the more electron-rich face of the double bond (stereoelectronic effect) [11]. Diastereoselective hydroboration of acyclic alkenes is one of the most successful results achieved by catalyzed hydroboration [10,12]. Rhodium-catalyzed hydroboration of allylic alcohol 4 yields a syn-adduct 6, whereas the uncatalyzed reaction of 9-BBN preferentially produces an anti-adduct 5 [12].…”

Hydroboration, Diboration, Silylboration, and Stannylboration

“…The remote substituent effect is not well understood, but the selectivity is highly depend- ent on the endo substituents, which will result in increased polarization of the neighboring double bond [79]. The diastereoselective hydroboration of acyclic alkenes is one of the most successful results achieved by catalyzed hydroboration (Scheme 1-17) [35,80,81]. The rhodium-catalyzed hydroboration-oxidation of allylic alcohol 64 [81] yields the syndiol, whereas the uncatalyzed reaction of 9-BBN preferentially produces the antidiol.…”

“…The diastereoselective hydroboration of acyclic alkenes is one of the most successful results achieved by catalyzed hydroboration (Scheme 1-17) [35,80,81]. The rhodium-catalyzed hydroboration-oxidation of allylic alcohol 64 [81] yields the syndiol, whereas the uncatalyzed reaction of 9-BBN preferentially produces the antidiol. The origin of diastereofacial selectivity arises from differences in the mechanism of π-complexation between the transition metals (65) and the main metals (67), together with the steric effect of the substituents (66) [81].…”

“…The rhodium-catalyzed hydroboration-oxidation of allylic alcohol 64 [81] yields the syndiol, whereas the uncatalyzed reaction of 9-BBN preferentially produces the antidiol. The origin of diastereofacial selectivity arises from differences in the mechanism of π-complexation between the transition metals (65) and the main metals (67), together with the steric effect of the substituents (66) [81]. The π-complexation of transition metals can be stabilized by the increased back-donation from a filled dorbital of the metal to a π*-orbital of alkene, which is enhanced when the best σ-acceptor adopts the anti position (65) and the smallest group (S) is in the inside crowded position (66).…”