Allyl carboranes

Also the radical species are easily formed on treatment of l-ethyl-2,3-dicyano-1,4-diazinium [188, 189] and 1-ethyl-1,2,4-triazinium salts [190] with nucleophiles, as evidenced by dimerization of pyrazinyl radicals into the corresponding dimeric structure (Scheme 63). It is worth noting that the synthetic potential of the intermediate radicals can be used as trapped with compounds bearing C-C double or triple bonds, for instance by reacting with allyl carboranes. The latter reaction is accompanied by the hydrolysis of one cyano group and results in the formation of the corresponding 2,5-diazabicyclo[2,2,2]octenes (Scheme 63) [189]. 

Allylation of the 10-carborane 236 (pKa = 18-22) with diallyl carbonate is possible under neutral conditions to give 237[146], Allylation and rearrangement of the trialkylalkynylborane 238 affords the trisubstituted alkene 239 stereoselectively [ 147],... 

Recently, the potential of 157Gd, which has a much higher cross sectional value than 10B for thermal neutrons has been of interest. Chelating agents, diethylene-triaminepentaacetic acid (DTPA) derivatives bearing carborane, were synthesized by the reaction of carboranyl allyl carbonate with DTPA ester. Treatment of... 

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. 

The C-allylation to ortho-carborane is accelerated by palladium catalysts. 

C-allylation is dependent on the ligand of palladium catalyst which assists the reaction of C-allylation to ortho-carborane. 

The solvent effect is high in the case of C-allylation to ortho-carborane cluster. In non-polar solvents the C-allylation is accelerated, while in polar solvents the C-allylation is decelerated. 

Desilylation. The mild conditions associated with the cleavage of the C-Si bond by TBAF are favorable to many synthetic processes that involve carbanions. The method has been applied to the alkylation of aldehydes with trimethylsilyl-o-carborane and to the allylation of sulfines. ... 

Allyl carbonates are particularly useful in alkylation of nucleophilic carbomnes both at the side chaint ] or directly at the carborane skeletonfi Hii72] .p. 

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