Boranes iodides

The reactions of trialkylboranes with bromine and iodine are gready accelerated by bases. The use of sodium methoxide in methanol gives good yields of the corresponding alkyl bromides or iodides. AH three primary alkyl groups are utilized in the bromination reaction and only two in the iodination reaction. Secondary groups are less reactive and the yields are lower. Both Br and I reactions proceed with predominant inversion of configuration thus, for example, tri( X(9-2-norbomyl)borane yields >75% endo product (237,238). In contrast, the dark reaction of bromine with tri( X(9-2-norbomyl)borane yields cleanly X(9-2-norbomyl bromide (239). Consequentiy, the dark bromination complements the base-induced bromination. 

BCl, BBr, and BI undergo exchange reactions to yield mixed boron hahdes. Exchange reactions also occur with trialkyl, triaryl, trialkoxy, or triaryloxy boranes and with diborane. Anhydrous metal bromides and iodides can be prepared by the exchange reaction of the metal chloride or oxide and BBr or BI (21)-... 

As mentioned in Sect. 3.1.1, secondary phosphine-boranes also react efficiently with aryl iodides in palladium-catalyzed substitution reactions (Pd(PPh3)4) [73]. In all cases the boranato functional group remains unchanged. 

The adducts derived from catechol borane are hydrolyzed by water to vinylboronic acids. These materials are useful intermediates for the preparation of terminal vinyl iodides. Since the hydroboration is a syn addition and the iodinolysis occurs with retention of the alkene geometry, the iodides have the -configuration.214... 

Bis(pyrazolyl)borate copper complex 47 has been employed as a catalyst in the homogeneous and heterogeneous styrene epoxidation reactions <00JCS(CC)1653>. Pyrazole palladacycles 48 have proven to be stable and efficient catalysts for Heck vinylations of aryl iodides <00JCS(CC)2053>. An asymmetric borane reduction of ketones catalyzed by N-hydroxyalkyl-/-menthopyrazoles has been reported <00JHC983>. 

Benzylic halides are reduced very easily using complex hydrides. In a-chloroethylbenzene lithium aluminium deuteride replaced the benzylic chlorine by deuterium with inversion of configuration (optical purity 79%) [537]. Borane replaced chlorine and bromine in chloro- and bromodiphenylme-thane, chlorine in chlorotriphenylmethane and bromine in benzyl bromide by hydrogen in 90-96% yields. Benzyl chloride, however, was not reduced [5iSj. Benzylic chlorine and bromine in a jy/n-triazine derivative were hydrogeno-lyzed by sodium iodide in acetic acid in 55% and 89% yields, respectively [5i9]. 

Alkyl radicals can be generated from alkyl iodides in a chain process initiated by a trialkylborane and oxygen.204 The alkyl radicals are generated by breakdown of a borane-oxygen adduct. 

Methylcryptaustoline iodide (14) was synthesized from phenylacetic acid 47 by Elliott (39) as shown in Scheme 7. Nitration of 47 to the 6-nitro compound 48 and reduction with sodium borohydride afforded lactone 49. Reduction of the aromatic nitro group with iron powder in acetic acid gave ami-nolactone 50, which was converted to tetracyclic lactam 51 with trifluoroacetic acid in dichloromethane. Reduction of the lactam by a borane-THF complex followed by treatment with methyl iodide afforded ( )-0-methylcryptaustoline iodide (14). 

The acid portion of 1 was assembled by enantio-and diastereocontrolled addition of Z-crotyl borane to the aldehyde 8, following the Brown protocol. Hydroboration and oxidation led to 9, which was condensed with the allenyl silane 10 to give 11 with high diastereocontrol. Conversion of the alcohol to the iodide followed by three-carbon homologation by the Myers procedure then led to 1, which was cyclized with > 10 1 regio- and diasterocontrol to give 12. Ozonolysis and methylenation of the less hindered ketone then delivered 3. 

EPOXIDES Alumina. r-Butyldimethyl-iodosilane. n-Butyllithium-Magnesium bromide. Cyclohexylisopropylamino-magnesium bromide. Dialkylaluminum amides. lodotrimethylsilane. Lithium l-a,a -dimethyldibenzylamide. Nafion-H. Organoaluminum compounds. Pyri-dinium chloride. Raney nickel. Tti-fluoroacetyl chloride, lrimethylsilyl-acctonitrile. Tris(phenylscleno)borane. Zinc iodide. 

ALCOHOLS Chlorotrimethylsilane-Sodium iodide. Iron carbonyl. Phenyl chlorothionocarbonate. Potassiurr>-18-Crown-6. Tri-n-bulyhin hydride. CARBONYL COMPOUNDS Bis(ben-zoyloxy)borane. Bis(triphenyIplios-pliine looppert I) te trahydrobora te. Cutecholborane. 

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