Alkylboron compounds

1- alkenyl triflates are carried out in the presence of KBr (1 equiv) to prevent decomposition of the catalyst [105]. 

2- alkylcarbapenems (46) were synthesized via coupling reaction of triflate 

Synthesis of 43 [111] To a solution of alkene (1.55 mmol) in THF (3 ml) was added 9-BBN (0.5 M in THF, 1.7 mmol) and the mixture was stirred for 4 h. In a separate flask, iodoalkene (1.92 mmol) was dissolved in DMF (5 ml). CS2CO3 (3.54 mmol) was then added with vigorous stirring followed by sequential addition of PdCl2(dppf) (0.198 mmol), Ph3As (0.2 mmol), H2O (0.42 ml), and finally the above borane solution. After being stirred for 2 h, the product was separated by chromatography over silica gel (77%). 

Synthesis of 45 [104] To a solution of iodoakane (0.35 mmol) in Et20 (5 ml) was added f-BuLi (1.7 M in pentane, 0.75 mmol) at -78 °C. After 3 min, 9-MeO-9-BBN (1 M in hexane, 0.82 mmol) was added followed by THF (5 ml). After being stirred for 10 min, the mixture was allowed to warm to room temperature over 1.25 h. Aqueous K3PO4 (3 M, 0.8 mmol), iodoakene (0.16 mmol) in DMF (5 ml) and finally PdCl2(dppf) 0.016 mmol) were added. The resultant dark solution was stirred for 16 h. 

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Solution polymerization of VDE in fluorinated and fluorochlorinated hydrocarbons such as CEC-113 and initiated with organic peroxides (99), especially bis(perfluoropropionyl) peroxide (100), has been claimed. Radiation-induced polymerization of VDE has also been investigated (101,102). Alkylboron compounds activated by oxygen initiate VDE polymerization in water or organic solvents (103,104). Microwave-stimulated, low pressure plasma polymerization of VDE gives polymer film that is <10 pm thick (105). Highly regular PVDE polymer with minimized defect stmcture was synthesized and claimed (106). Perdeuterated PVDE has also been prepared and described (107). 

The reaction of [ Co"(DMG)2py 2] with B( -C4H,)3 in benzene followed by extraction with CH2Cl2/aq. NaOH produces [ -BuCo(DMG)2py] the reaction is less successful with [pyCo "(DMG)2Cl] 161). This may be a convenient method using the more stable arylboron derivatives, but is probably experimentally more difficult than the Grignard route if a lower alkyl is to be introduced, because the lower alkylboron compounds inflame spontaneously in air, though they do not react with water, while the aryls are stable in air. 

Perillyl aldehyde (entry 11 in Table 13.3) is typically obtained from the corresponding alcohol via Oppenauer-type oxidation by using alkylboron compounds... 

Other interesting electrolytic systems have been developed based on electrolysis of triethylsulfonium bromide in acetonitrile with a lead cathode H8,ii9)j and electrolyses of aqueous solutions of sodium tetra-alkylboron compounds 245,337) Altogether, the breadth and depth of the research effort that has been devoted to the various electrolytic methods for the synthesis of tetraalkyllead compounds is remarkable. However, the successful development of a commercial process has not been accomplished, and indeed, it is probably less likely today than it was several years ago. 

At the root of the instability of fluoroaUcylboron compounds is the availability of a vacant orbital on boron it will be seen that when boron is co-ordinately saturated, as in four-covalent boron derivatives (10.26A), or partially saturated by tt bonding with attached oxygen- or nitrogen-containing groups (10.26B), then the stability of perfluoro-alkylboron compounds increases (Figure 10.26). 

The addition of dialkyboranes such as 9-borabicyclo[3.3.1Jnonane (9-BBN), disiamylborane, or dicyclohexylborane to I-alkenes gives alkylboron compounds [12]. The... 

For the synthesis of trialkylboranes. hydroboration is carried out with a borane solution in THF or with the borane-methyl sulfide complex (BMS) in THF, diethyl ether, or dichloromethane. Diborane reacts rapidly and quantitatively with alkenes to produce a solution of trialkylborane [16] (eq (13)). The addition of dialkylboranes. such as 9-borabicyclo[3.3.1]nonane (9-BBN. 3). disiamylborane (1), or dicyclohexylb-orane (2), to alkenes or alkynes gives mixed alkylboron compounds. The high regio-. stereo-, or chemoselectivity in the additions of these borane reagents unsaturated C—C bonds have been extensively used in organic syntheses. 

Despite the low intrinsic reactivity of alkylboranes, Pd-catalyzed all lation with alkylboron compounds holds considerable promise as a unique and chemoselective alkylation method. It is unique in part because hydioboration of alkenes is by far the most general and dependable method for stoichiometrically converting alkenes into organometals and in part because alkylboron compounds thus generated can satisfactorily participate in Pd-catalyzed alkylation under basic conditions. In this connection, it should be noted that the current scopes of hydroalumination and hydiozirconation of alkenes are much more limited than... 

Because the oxidation step in the hydroboration-oxidation synthesis of alcohols takes place with retention of configuration, the hydroxyl group replaces the boron atom where it stands in the alkylboron compound. The net result of the two steps (hydroboration and oxidation) is the syn addition of —H and —OH. We can review the anti-Markovnikov and syn aspects of hydroboration-oxidation by considering the hydration of 1-methylcyclopentene, as shown in Fig. 8.3. 

The first synthetic method developed for preparing boron-carbon rings involved the use of organometallic compounds (7). Currently, this preparation is only of historical interest, so far as alkylboron compounds are concerned, but it is still important in the synthesis of arylborane hetero-cyclics. C6H5BF2 and a,w-dilithioalkanes react to form simple B-phenyl-boracyclanes (XXVIII). 

Tabl 31.2 Coupling reaction of iodobenzene with various alkylboron compounds [2]... 

Abe, S. Miyaura, N. Suzuki, A. 1992. The palladium-catalyzed cross-coupling reaction of enol acetates of a-bromo ketones with 1-alkenyl-, aryl-, or alkylboron compounds A facile synthesis of ketones and their enol acetates. J. Am. Chem. Soc. 65 2863-2865. 

The addition of B pin to activated alkenes is an efficient way to generate alkylboronates. One version of this reaction entailed the use of a platinum complex to catalyze the addition, which generated remarkably high yields of the boronates when heated (Scheme 6.6) [12, 13]. While there was some substrate specificity, this was an effective approach to the synthesis of alkylboronate compounds from Michael acceptors. It should be noted that a chiral imidazolinium salt catalyzed the enantioselective borylation of acyclic enones with excellent selectivity (up to er=98 2 [ 14]). The copper-catalyzed borylation of cyclopropenes has also been reported using bisphosphine as the chiral ligand (Schanes 6.7 and 6.8) [15,16] in... 

Although clearly of use in the synthesis of certain alkylboron compounds, particularly tri-n-alkylboranes and alkylboron hydrides, the hydroboration reaction (developed mainly by H. C. Brown) is of considerable significance in synthetic organic chemistry, as the resulting organoboron compound can be used (without being isolated) as an intermediate in the conversion of olefins or acetylenes into other hydrocarbons (parafi or olefins), alcohols, aldehydes, ketones, carboxylic acids or amines. 

The copper-catalysed y-selective coupling between propargylic phosphate (83) and alkylboron compound (84) afforded chiral multisubstituted allenes (85) with various functional groups (Scheme 20). ... 

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