Hydroboration followed by oxidation

Addition of the elements of water to a double bond can be achieved through hydroboration, followed by oxidation and hydorlysis of the organoboron... 

Awfi-Markownikov hydration of alkenes may be effected indirectly by addition of 82Hg (hydroboration), followed by oxidation of the... 

RCH—CHi - RCHiCHO. This reaction can be carried out by hydroboration followed by oxidation of the resulting organoborane with pyridinium chlorochro-mate (PCC). In first reports of the transformation BH3 S(CII3)2 was used, but this hydroboration is not regiospecific in the case of terminal alkenes. Use of disiamylborane is superior since this borane is highly selective in hydroboration of both alkenes and dienes.1... 

The conversion of an alkene into the corresponding ketone may be effected by means of a convenient sequence which involves hydroboration followed by oxidation with chromic acid of the resulting organoborane (cf. Section 5.4.3,... 

Asymmetric hydroboration followed by oxidation is used to give optically active alcohols. For example, addition of (+)-IpcBH2 to 1-phenylcyclopentene followed by oxidation gives S,2R)-trans-2-phenylcyclopentanol in 100% e.e. (Equation B2.9). The structure of the product alcohol reveals that the homochiral hydroborating reagent encounters fewer unfavourable steric interactions with alkene substituents if it approaches the lower face of the alkene as drawn in Equation B2.9. This preference determines the absolute stereochemistry of the product. (The regiochemistry and relative stereochemistry of the product are determined by fundamental hydroboration characteristics.)... 

Aldehydes, RCHO (Sec. 7.9) (Sec. 7.9) (Sec. 8.4) (Sec. 17.7, 19.2) (Sec. 19.2, 21.6) from disubstituted alkenes by ozonolysis from 1,2-diols by cleavage with sodium periodate from terminal alkynes by hydroboration followed by oxidation from primary alcohols by oxidation from esters by reduction with DIB AH [HA1(i-Bu)2]... 

Oxetanes. The reaction of ketones with 3 equiv. of the sodium anion (2) of 1 results in exclusive or predominant formation of the thermodynamically more stable oxetane. For example, axially C—O-bonded oxetanes such as 3 are formed from unhindered cyclohexanones. The reagent 1 can therefore serve as a CH,CH, synthon. Thus reaction of 3 with aqueous HC1 in THF yields a single homoallylic alcohol (4). It (3) is converted into the alcohol 5 in 93% yield on hydroboration followed by oxidation. The oxetane ring is opened by a few other nucleophiles [C6H5SNa, HMPT, (CH3)2CuLi], but is inert to several other nucleophiles, such as QH5SCH2Li and LiCH2C02C(CH3)3. 

Problem 7.11 T he following cycloalkenc gives a mixture of two alcohols on hydroboration followed by oxidation. Draw the structures of both, and explain the result. 

Hydroboration followed by oxidation provides an indirect route for hydration of diynes and constitutes an efficient route to acetylenic ketones as demonstrated by the synthesis of 206 in 75% yield from diyne 205... 

Hydroboration, followed by oxidation using alkaline hydrogen peroxide, results in overall anti-Markovnikov addition of water. 

In contrast to the oxidative deavage of the C10-C11-moiety, hydroboration followed by oxidation furnishes Cll-functionalized quinine and quinidine derivatives. As an illustration, only transformations in the quinidine series are shown (cf. Scheme 12.14). Cll-aldehyde 58 was obtained either upon direct oxidation of the borane species with PCC/Si02 or via an improved stepwise procedure including (i) oxidation with Me3NO-2 H20 to yield the terminal alcohol 57 and (ii) subsequent Dess-Martin oxidation [35], Oxidation and esterification of alcohol 57 using Jones reagent and MeOH/HCl gave the Cl 1-ester 59, which is a suitable precursor for the synthesis of cinchona alkaloid macrocycles (Scheme 12.15) [38],... 

Although water, in some cases, has undergone addition across the C-C double bond in a vinylcyclopropane under acidic, - neutral, " and basic " - aqueous conditions, e.g. formation of 2, the reaction has more often been performed using a two-step procedure. Most frequently used was a one-pot synthesis consisting of hydroboration followed by oxidation with hydrogen peroxide/sodium hydroxide. The alkylboranes, formed in the first step, can be isolated. - The first step has generally been carried out using diborane in tetrahydrofuran 398,410,430,745,852,1025,1590,1609,1793,1833.1877-1884 9-borabi-... 

A stepwise, double hydroboration followed by oxidation on 258 gave a mixture of hydroxy aminoboranes 264 in 90% yield, which was oxidized with PCC to the keto-aminoborane 265. Isomerization with N-tert-butyl-... 

The aldehyde 73 was prepared from diacetone D-mannose 72 in 80% overall yield (Scheme 9) Treatment of 73 with allyltrimethylsilane followed by benzylation gave the benzyl ether 74. Opening of the furanoside ring gave the hydroxyalkene 75 (78%), which underwent hydroboration followed by oxidation of the resulting diol to afford the ketoaldehyde 76. Removal of the p-methoxybenzyl group with DDQ provided 77, which... 

The oxidative hydration of alkenes to aldehydes or ketones is most often achieved on the laboratory scale in two steps by hydroboration followed by oxidation of the intermediate alcohol. 

Longifolene on hydroboration followed by oxidation with alkaline hydrogen peroxide furnishes, in 74% yield, essentially pure longifolol (57) as a result of endo attack (46). On the other hand, camphene, under the same treatment, is known (47) to give almost exclusively endo-iso-camphanol (58) by way of exo approach of the reagent. Oxidation of longifolyl-borane with air or silver oxide results in transannular products which are discussed in a later section. 

Alkenes can be hydrated to form alcohols by (1) hydroboration followed by oxidation with alkaline hydrogen peroxide and (2) acid-catalyzed hydration. Compare the product formed from each alkene by sequence (1) with those formed from (2). 

Acid-catalyzed hydration (Section 7.7B) of 1-ethynylcyclohexanol gives an a-hydroxyketone. Alternatively, hydroboration followed by oxidation with... 

Oxymercuration/demercuration has thus been suggested as a mild procedure for the Markovnikov hydration of carbon-carbon double bonds. As shown in Chapter 3, hydroboration followed by oxidation can be used for their hydration contrary to Markovnikov s rule. The two reaction sequences are compared below for 1-hexene ... 

Neither the mesylate nor the tosylate derived from 12 could be induced to cychze. In contrast, intramolecular displacement of the iodide proceeded well, to give 13. Hydroboration followed by oxidation then gave 15, which on deprotection cyclized to (-l-)-fawcettimine 3. 

As shown earlier by Chung et al. [33], Lee and Han [34] found that the double bond in a PI having predominantly 1,4-addition microstructure was very difficult to introduce hydroxyl groups. They first synthesized, via anionic polymerization, a nearly monodisperse PI having 34% 1,2-addition, 59% 3,4-addition, and 7% 1,4-addition in tetrahydrofuran (THF) as solvent. Subsequently, the PI was hydroborated followed by oxidation according to the procedures detailed in a paper by Lee and Han [34], yielding... 

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