Alcohols hydroboration-oxidation

Hydrate to alcohol hydroborate/oxidize (THF/B2H5,H202/0H-) (syn, anti-Markovnikov)... 

Hydroboration-oxidation of a pinene (page 235) like catalytic IS stereoselective Addition takes place at the less hindered face and a single alcohol is produced in high yield (89%) Sug... 

Hydroboration-oxidation of (E) 2 (p anisyl) 2 butene yielded an alcohol A mp 60°C in 72% yield When the same reaction was performed on the Z alkene an isomenc liquid alcohol B was obtained in 77% yield Suggest reasonable structures for A and B and describe the relation ship between them... 

Methyl-2-hexcne has a disubstituted double bond, RCH=CHR, and would probably give a mixture of two alcohols with either hydration method since Markovnikov s rule does not apply to symmetrically substituted alkenes. 3-MethyI-3-hexene, however, has a trisubstituted double bond, and would give only the desired product on non-Markovnikov hydration using the hydroboration/oxidation method. 

Draw the structures of alkenes that would yield the following alcohols on hydration (red - O). Tell in each case whether you would use hydroboration/ oxidation or oxymercuration. 

Application of the hydroboration transform to intermediate 5 provides unsaturated alcohol 6 as a potential precursor. In the synthetic direction, a regio- and stereocontrolled hydroboration/oxidation of the A5 6 double bond in 6 could accomplish the simultaneous introduction of the adjacent C-5 hydroxyl- and C-6 methyl-bearing... 

With ring G in place, the construction of key intermediate 105 requires only a few functional group manipulations. To this end, benzylation of the free secondary hydroxyl group in 136, followed sequentially by hydroboration/oxidation and benzylation reactions, affords compound 137 in 75% overall yield. Acid-induced solvolysis of the benzylidene acetal in 137 in methanol furnishes a diol (138) the hydroxy groups of which can be easily differentiated. Although the action of 2.5 equivalents of tert-butyldimethylsilyl chloride on compound 138 produces a bis(silyl ether), it was found that the primary TBS ether can be cleaved selectively on treatment with a catalytic amount of CSA in MeOH at 0 °C. Finally, oxidation of the resulting primary alcohol using the Swem procedure furnishes key intermediate 105 (81 % yield from 138). 

Use of the reagent diisopinocampheylborane SO (prepared by treating optically active a-pinene with BH3) results in enantioselective hydroboration-oxidation. ° Since both (-I-) and (-) a-pinene are readily available, both enantiomers can be prepared. Alcohols with optical purities as high as 98% have been obtained in this... 

Hydroboration-oxidation of 1,4-di-f-butylcyclohexene gave three alcohols 9-A (77%), 9-B (20%), and 9-C (3%). Oxidation of 9-A gave a ketone 9-D that was readily converted by either acid or base to an isomeric ketone 9-E. Ketone 9-E was the only oxidation product of alcohols 9-B and 9-C. What are the structures of compounds 9A-9E ... 

A biomimetic synthesis of benzo[c]phenanthridine alkaloids from a protoberberine via the equivalent of a hypothetical aldehyde enamine intermediate has been developed (130,131). The enamide 230 derived from berberine (15) was subjected to hydroboration-oxidation to give alcohol 231, oxidation of which with pyridinium chlorochromate afforded directly oxyche-lerythrine (232) instead of the expected aldehyde enamide 233. However, the formation of oxychelerythrine can be rationalized in terms of the intermediacy of 233 as shown in Scheme 41. An alternative and more efficient... 

Alcohols from Alkenes Through Hydroboration-Oxidation... 

The uncatalyzed hydroboration-oxidation of an alkene usually affords the //-Markovnikov product while the catalyzed version can be induced to produce either Markovnikov or /z/z-Markovnikov products. The regioselectivity obtained with a catalyst has been shown to depend on the ligands attached to the metal and also on the steric and electronic properties of the reacting alkene.69 In the case of monosubstituted alkenes (except for vinylarenes), the anti-Markovnikov alcohol is obtained as the major product in either the presence or absence of a metal catalyst. However, the difference is that the metal-catalyzed reaction with catecholborane proceeds to completion within minutes at room temperature, while extended heating at 90 °C is required for the uncatalyzed transformation.60 It should be noted that there is a reversal of regioselectivity from Markovnikov B-H addition in unfunctionalized terminal olefins to the anti-Markovnikov manner in monosubstituted perfluoroalkenes, both in the achiral and chiral versions.70,71... 

Ligand 73 was prepared directly from a single enantiomer of the corresponding naphthol of QUINAP 60, an early intermediate in the original synthesis, and both enantiomers of BINOL. Application in hydroboration found that, in practice, only one of the cationic rhodium complexes of the diastereomeric pair proved effective, (aA, A)-73. While (aA, A)-73 gave 68% ee for the hydroboration of styrene (70% yield), the diastereomer (aA, R)-73 afforded the product alcohol after oxidation with an attenuated 2% ee (55% yield) and the same trend was apparent in the hydroboration of electron-poor vinylarenes. Indeed, even with (aA, A)-73, the asymmetries induced were very modest (31-51% ee). The hydroboration pre-catalyst was examined in the presence of catecholborane 1 at low temperatures and binuclear reactive intermediates were identified. However, when similar experiments were conducted with QUINAP 60, no intermediates of the same structural type were found.100... 

Cationic rhodium complexes of these ligands were prepared and applied in the enantioselective hydroboration-oxidation of a range of vinylarenes,106,107 carefully chosen to highlight the effect on reactivity and enantioselectivity of different aryl substituents and / -substitution. Like QUINAP 60 and PHENAP 65, the ( -ligand gave rise to the (A)-secondary alcohol. 

The oxidation of hexahydroindolo[2,3-a]quinolizin (574) with benzoyl peroxide, followed by reduction and removal of the benzoyl group, gave the cis alcohol (575), while hydroboration-oxidation of the same enamine (574) yielded... 

Olefins, conversion to alcohols, 53, 94 from tosylhydrazones and methyllithium, 51, 69 hydroboration-oxidation of,... 

Halogen-lithium exchange of iodide 71 and subsequent addition of 2-acetyl-furan (72) to the resultant organolithium intermediate yielded two diastereomeric tertiary alcohols (dr=l l), which were converted to (E)-olefin 73 with complete diastereoselectivity upon brief exposure to catalytic amounts of concentrated aqueous hydrogen chloride (Scheme 11) [18]. Diastereoselective hydroboration/oxidation of 73 gave largely the desired stereoisomer 74 due to... 

The iodoetherification strategy was applied to the synthesis of the smaller fragment coupling component 109 as well (Scheme 16). Silylation of alcohol 104 [30] (76% de) allowed the separation of the pure desired diastereomer, which in turn was subjected to hydroboration/oxidation, sulfide formation with thiol 105, and oxidation to give sulfone 106. The requisite y-triethylsilyloxy alkene functionality in 107 was constructed as a diastereomeric E) Z)=l.2 l mixture by another sulfone-based olefination of aldehyde 90 with 106. Treatment of 106 with... 

A hydroboration-oxidation sequence has been described for the desymmetrization of bicyclic hydrazino-alkenes. The use of BDPP as a chiral ligand on Rh provides the desired alcohol in 84% ee, following oxidation of the hydroborated... 

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