TELLURIUM-MEDIATED HALOGEN TRANSFER FROM POLYHALOALKANES TO DIYNE ACCEPTORS

Elemental tellurium catalyzes transfer of halogen from (CHCl2)(2), from C2HCl5 and from (CHBr2)(2), to the phenylated diynes 1-3, 17, 20, and 24, in which the alkyne moieties are in close proximity. The process is associated with cyclorearrangement reactions by which halogenated polycycles are formed. In boiling C2HCl5, derivatives of 1,2-bis(phenylethynyl)benzenes afford 5-halogenated indeno[2,1-a]indenes, 1,8-bis(phenylethynyl)naphthalene gives a chlorinated benzo[k]fluoranthene derivative, and 2,2'-bis(phenylethynyl)[1,1'-biphenyl] forms 9-chloro-14-phenylbenz[a,c]anthracene. Diynes 25 and 26 in which the ethynyl functions are further removed from each other fail to yield halogenated products. Diyne 25 undergoes oxidative cyclization by which 1,3-diphenyldibenzo[3,4:6,7]cyclohepta[1,2-c]furan (29) is formed. Compound 26 is transformed to hydrocarbon 32, which involves a phenyl ring walk and elimination of H2Te.