Carboranes benzyl

Nemoto, Yamamoto, and Cai[30a] later modified the preparation of their water-soluble carborane to include the attachment of a tumor seeking uracil moiety (Scheme 5.8). Key transformations allowing the synthesis of this unique dendritic carborane (33) included construction of masked uracil allyl carbonate 34 and its subsequent connection to the benzyl protected o-carborane cascade 35, the intermediate precursor to tetraol 30, via palladium bis(dibenzylideneacetone) [Pd(dba)2] and l,2-bis(diphenylphosphino)ethane (dppe) mediation. 

We found that the methylene group in l-methyl-2-benzyl-o-carborane is highly acidic (pKa = 19.5). Its acidity is even higher than acidity of o-carborane (pKa=23.3) and 1 -methyl-7-benzyl-/w-carborane (pKa = 33.5). 

Under the action of BuLi on substituted benzyl-o-carboranes (13-15) metallation on the CH2 group occurs readily to give coloured lithium benzyl-o-carboranes (16-18) that are less soluble in aprotic solvents than lithium-o-carboranes. 5... 

The lithiumbenzyl carboranes readily react with various electrophilic reagents. This was shown by taking a lithium derivative 17 as an example (Scheme 4). The reactions proceed in high yields and make it possible to obtain various derivatives of o-carborane containing a substituted benzyl group. 

Based on the benzyl derivative (26), the first stable carborane-containing simple enol (27) was synthesized2 (Scheme 8). The acid chloride (28) readily enters into a Friedel-Crafts reaction with mesitylene to give ketone (29). Under the action of BuLi on a benzene-ether solution of ketone (29) enolate (30) is formed. Treatment of the latter with diluted HC1 solution results in enol (27). Starting from the benzyl derivative (31), carboranyl-substituted indene (32) was synthesized by intramolecular cyclization with a formation of ketone (33), whose reduction (34) followed by dehydration results in (32) (Scheme 9). 

Ortfto-carborane clusters can be functionalized at both the boron and carbon atoms of the cages. Selective functionalization of ortfto-carborane clusters can be achieved at the B(9) boron atom via electrophilic alkylation with alkyl halides and benzyl halides that contain electron-withdrawing... 

Zakharkin, L. L Olshevskaya, V. A. 1995. Synthesis of 9-benzyl-o- and 9-benzyl-m-carboranes containing functional substituents in the benzene ring by electrophilic alkylation of o- and m-carboranes by the corresponding R-benzyl hahdes. Rmm. Chem. Bull.,A4 1099-1101. 

In order to avoid the degradation of the dendrimer, a benzyl ether group was used as the protecting group to obtain the carborane synthon shown in Scheme 27.6. In addition, the core of the... 

In 1990, Gabel and coworkers reported the synthesis of carboranylporphyrins in which the carborane cluster is linked to the porphyrin via carbon-carbon bonds through a benzyl group. Later, Vicente et al. used a similar strategy to prepare carboranylporphyrins. In both cases, tetraarylpor-phyrins (para- and mew-substituted) containing four or eight l-CH3-l,2-c/oso-C2B,oH,o, not directly... 

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