1,2-Dehydro-o-carborane

Dehydrobenzene or benzyne 158 can be trapped by all manner of species. 1,2-Dehydro-o-carborane 159 has been shown to undergo many of the same reactions as its two-dimensional relative, 1,2-dehydrobenzene. Although dehydroaromatic molecules can be formed in a variety of ways, synthetic pathways to 1,2-dehydro-o-carborane are quite limited. An effective procedure reported so far78 first forms the dianion by deprotonation of o-carborane with 2 equiv. of butyllithium. Precipitated dilithium carborane is then treated with 1 equiv. of bromine at 0°C to form the soluble bromo anion 160. Thermolysis of 160 with anthracene, furan, and thiophene as substrates leads to the adducts 161-164.79 80 1,2-Dehydro-o-carborane reacts with norbomadiene to give both homo 2+4 and 2+2 addition, leading to three products 165-167, in a 7 1 ratio79. An acyclic diene, 2,3-dimethyl-... 

Figure 54 The ene reaction (89) and 2+2 reaction (90) products obtained from reaction between 1-phenyl-1-propyne (87) and 1,2-dehydro-o-carborane (88). (Adapted from ref. 121.)...

Pd/Ni-COCATALYZED [2 - - 2 - - 2] CYCLOADDITION OF 1,3-DEHYDRO-o-CARBORANE WITH ALKYNES... 

In an initial attempt, the B NMR spectrum showed almost quantitative formation of 1-methyl-o-carborane upon heating a toluene solution of l-Li-2-Me-3-I-l,2-C2BioH9 in the presence of 10mol % of Pd(PPh3)4. This catalytic deiodination process may be due to the thermal decomposition of Pd-2-methyl-1,3-dehydro-o-carborane presumably via a radical process under thermal conditions [14], in which the solvent acts as the hydrogen source. 

PD/NI-COCATALYZED [2 + 2 + 2] CYCLOADDITION OF 1,3-DEHYDRO-O-CARBORANE WITH ALKYNES 87... 

Scheme 7.8 Pd/Ni co-catalyzed [2 + 2 + 2] cycloaddition of 1,3-dehydro-o-carborane with alkynes.

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