Boranes dicyclohexylborane

LiAlH, NaAlH, Thexylborane Al-compds., organo-R2BH, Bis-(3-methyl-2-butyl)-borane, Dicyclohexylborane, D i(isopinocamphey I) borane, 9-Borabi-cycio[3.3.1 Jnonane Na[AlH2(i-C Hg)2]... 

In the hydroboration of terminal alkenes, carrying a ketone or aldehyde group, with a variety of borane reagents, dicyclohexylborane has been identified as the most efficient reagent. Analogous hydroboration of alkynyl ketones and alkynyl aldehydes with dicyclohexylborane yields the corresponding olefinic carbonyl compounds after protonation, or dicarbonyl compounds after oxidation. ... 

Tris(glycosyl)boranes and dicyclohexylboranes are iodinated with Nal/Chloramine T or brominated with NaBr/Chloramine T to yield iodinated and brominated sugars, respectively946. BC13 is used for the selective chlorination of carbohydrates947. 

The synthesis of 9-alkenyl-9-BBN via hydroboration of terminal alkynes with 9-BBN suffered from the formation of 1,1-diborylalkanes via dihydroboration along with desired monohydroboration products. Alternatively, selective monohydroboration of terminal alkynes with dicyclohexylborane was followed by transmetallation with 9-MeO-9-BBN (Equation (193)).710 Treatment of the hydroboration intermediates with DIBAL-H in the presence of a borane-trapping reagent such as 1-hexene gave 1-alkenylaluminum compounds with complete retention of the (E)-stereochemistry (Equation (194)).711... 

The mildness of these reagents tolerates the presence of various functional groups such as ester, ether, halogen, and nitrile. The stereospecific cis nature of hydroboration gives exclusively the tram alkenylboranes, often also in high regioisomeric purity (Eq. 53). On the other hand, highly pure (Z)-l-alkenyl-dialkylboranes are prepared without any difficulty via the monohydroboration of 1-halo-1-alkynes with disiamyl-borane or dicyclohexylborane, followed by treatment with t-butyllithium (Eq. 55)106). 

Hydroboration of allenes. With few exceptions, the 9-BBN hydroboration of allenes affords B-allylic-9-BBN derivatives. In contrast, the reactions of allenes with disiamylborane or dicyclohexylborane afiord predominantly vinylic boranes. With unsymmetrical allenes, 9-BBN binds to the less substituted carbon atom. Allene itself affords a 1,3-dibora derivative. The B-allylic-9-BBN derivatives are useful reagents for the allylic boration of carbonyl compounds. ... 

Conjugated cis,cis-d ieney. Dihydroboration of a conjugated diyne, for example dodcca-5,7-diyne (1), with dicyclohexylborane followed by protonolysis of the organo-borane intermediate with acetic acid leads to a conjugated di.cu-diene (rw.t is-dodeca-... 

Conjugated diynes can be reduced to cis enynes by the well-known hydroboration-protonolysis sequence . cw-5-Dodecen-7-yne (215) is obtained from the diyne 213 in 76% yield as shown in equation (23). The orientation of addition of the disiamyl-borane was established by using CH3CO2D in the second step. Addition of a second mole of disiamylborane to 214 is very slow, but reduction to the cis,cis diene can be accomplished by using dicyclohexylborane instead . 

HYDROBORATION Bis-3-methyl-2-butyl-borane. Diborane. Dicyclohexylborane. Trimethylamine oxide. 

With hydride reagents such as dibal, Z-alkenes can be selectively obtained from alkynes in the phenolic lipid series (ref. 162), and related series of boron reagents greatly supplement the chemical methods of selective reduction and alkyiation. This selectivity has been achieved by the use of less reactive dialkylboranes such as bis(3-methyl-2-butyl)borane (di-isoamylborane), bis(2,3-dimethyl-2-butyl)borane (thexylborane), 9-boraUcyclo[3.kl]nonane (9-BBN) and dicyclohexylborane. Some applications in the polyethenoid field have been summarised (refs. 135,163) and the synthesis of alkenyl compounds generally reviewed (ref. 164). By the use of dibromoborane dimethylsulphide, an internal alkyne can be reduced selectively (ref. 165) as for example in the following way (R = n-alkyl). 

Vinylboranes are versatile intermediates, and there are modifications that convert them to alkenes. Hydro-boration of a terminal alkyne such as cyclohexyl acetylene (78) with dicyclohexylborane gave ( )-alkenyl-borane (79). Subsequent treatment with iodine and sodium hydroxide resulted in transfer of an alkyl group from boron to the alkenyl carbon, generating cis-1,2-dicyclohexylethene (80) in 77% yield (92% isomeric... 

RCH=CH2- RCH2C00H. This conversion can be effected in >80% overall yield by hydroboration of 1-alkenes with HBBr2 S(CH3)3, H2BBr S(CH3)2, thexyl-borane (H2BThx), or dicyclohexylborane (HBChx2), followed by hydrolysis to form RCH2B(0H)2. The final step is oxidation of RCH2B(OH)2 to RCOOH, which can be... 

The hydroboration of heterocyclic olefins having oxygen [50-56], sulfur [57], and nitrogen [58-68] are reported. Brown and coworkers [69] have conducted detailed hydroboration studies of many heterocyclics with an endocyclic double bond with borane-methylsulfide BMS, 9-BBN, CtuqBH, and SiajBH and have established the optimum conditions for clean and quantitative hydroboration. The hydroboration of 2,3- and 2,5-dihydrofuran with BMS (3 1 molar ratio) at 25 °C for 1 h afibrds trialkylborane, readily oxidized to 3-hydroxytetrahydro-furan, in excellent yield. But the synthesis of dialkylboranes from these olefins using olefins, BMS in 2 1 ratio is not possible at 0 °C. However, hydroboration of 2,3-dihydrofuran proceeds cleanly with 9-BBN in 1 1 ratio and oxidation affords the desired 3-hydroxytetrahydrofuran, in excellent yield. Similar results are obtained with dicyclohexylborane and disiamylborane (Table 5.14). 

The monohydroboration of terminal alkynes with dicyclohexylborane, disiam-ylborane, catecholborane, and dimesitylborane, and complexes of dihaloboranes and 9-BBN provides the simple and efficient route to fra s-vinylboranes [1,2]. Unlike other dialkyl(vinyl)boranes, vinyl-9-BBN derivatives exhibit remarkable stability [3, 4]. However, with 1 1 stoichiometry of terminal alkyne 9-BBN, 9-BBN adds twice to give a significant amount of diboryl adduct (Eq. 5.19) from which boron stabilized carbanion can be made [5, 6]. The partial solution to dihydroboration is achieved either by employing 100% excess of the alkyne [3] or using silylated derivatives [4e, h]. 

The hydroboration-oxidation studies of 1,4-epoxy-1,4-dihydronaphthalene (1) with various hydroborating agents such as borane-methyl sulfide (BMS), dicy-clohexylborane, disiamylborane, and 9-BBN have yielded interesting results [1]. The reaction of 1 with dicyclohexylborane or disiamylborane affords the exo alcohol 2 without epoxy ring opening (Eq. 32.1). On the other hand, 9-BBN hy-droboration of 1 (1 1 mole ratio) in THE at 25 °C, followed by oxidation affords a homoallylic alcohol 3 after opening of the epoxy ring (Eq. 32.2). BMS, however, affords a mixture of both the alcohols. 

Several papers have appeared describing the synthesis of alkyl halides from organoboranes. Alkyl chlorides are obtained by the reaction of trialkylboranes with dichloramine-T, and in somewhat lower yield with iV,N-dichlorourethane/ whereas alkyl bromides are produced in excellent yield when the boranes derived from terminal alkenes and dicyclohexylborane are treated with either Bt2 or BrCl. Alkyl iodides are obtained from the same boranes by the use of ICl-NaQAc " or iodide ion-chloramine-T/ and this latter method has been applied to the radioiodination of olefins (with Vinyl iodides result from... 

Terminal alkynes are hydroborated in a regioselective, anti-Markovnikov fashion, the boron attacking the less hindered carbon. However, with borane itself, this reaction leads ultimately to sequential hydroboration of both tt bonds. To stop at the alkenylborane stage, bulky borane reagents, such as dicyclohexylborane, are used. 

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