1,1.1-Trihalides 1,3-heterocyclics

N-Bridged tellurium-containing heterocycles are exemplified by derivatives of l,4-tellurazine[2,3-g/i]carbazole 107 and heterocycle 108. One-pot reaction of A-propargylcarbazole with tellurium tetrahalides under conditions of the two-phase tellurohalogenation (Section n,B,l) leads to halogenomethylene derivatives 107 (90KGS126). The reaction proceeds as the spontaneous electrophilic cycliza-tion of initially formed tellurium trihalides 109. 

Although 1,3,2-diazaphospholenium cations are usually prepared from neutral NHPs or 1,3,2-diazaphospholes via Lewis-acid induced substituent abstraction or A-alkylation, respectively (cf. Sect. 3.1.2), the group of Cowley was the first to describe a direct conversion of a-diimines into cationic heterocycles by means of a reaction that can be described as capture of a P(I) cation by diazabutadiene via [4+1] cycloaddition [31] (Scheme 4). The P(I) moiety is either generated by reduction of phosphorus trihalides with tin dichloride in the presence of the diimine [31] or, even more simply, by spontaneous disproportionation of phosphorus triiodide in the presence of the diimine [32], The reaction is of particular value as it provides a straightforward access to annulated heterocyclic ring systems. Thus, the tricyclic structure of 11 is readily assembled by addition of a P(I) moiety to an acenaphthene-diimine [31], and the pyrido-annulated cationic NHP 12 is generated by action of appropriate... 

Cyclizations with perfluoroacylating agents seem to be quite general for the synthesis of 5(2i7)-oxazolones with aromatic substituents directly bonded to the heterocyclic ring. For example, perfluoroacylation of a solution of an arylgly-cine containing a phosphorus trihalide affords 4-aryl-2-(perfluoroalkyl)-5(2//)-oxazolones (Table 7.1, Fig. 12) Similar results were obtained when amino nitriles were used as starting materials. ... 

The reagents most frequently used to reduce the A-oxides to the parent heterocycle are trivalent phosphorus compounds. These include the phosphorus trihalides, usually in chloroform or ethyl acetate, triphenylphosphine, and phosphite esters such as triethyl phosphite. Substituents which are easily reduced are not affected, although nitro groups... 

In general, deoxygenation of heterocyclic JV-oxides is effected by the use of phosphorus trihalides or by catalytic reduction with Raney nickel.312 Because of their higher selectivity the phosphorus reagents are preferable. In the pyrido[2,3-a ]pyrimidine series, 3-oxides are deoxy-genated in moderate yield by phosphorus trichloride, by Raney nickel,309 or by titanium(III) chloride. 4... 

C-atom 44, 576 2-siloxy-1,1,1 -trihalides, with 1 extra C-atom 43, 909 sulfonylhydrazones 44, 308 y-sulfonyl-5-lactones 44,192 2,2,2-trifluoroalcohols44, 542, 577 4-Oxo-1,3-heterocyclics... 

The boron hydride-catalyzed exchange reaction is not limited to tri-organoboranes or boron heterocyclics. Boron trihalides readily exchange with organoboranes at low temperatures (12). Reaction of BCI3 with 1,4-... 

The first instance of an aluminum trihalide adduct with an Af-heterocyclic carbene was reported in 2004 (phosphanylsilylcarbene adducts had previously been reported [128]). The adduct and its gallium analog were prepared from the reaction of ImMe4 with aluminum trichloride or gallium trichloride in toluene the aluminum complex was crystallographically characterized [129]. Later, NHC adducts of AII3 were also structurally characterized [130]. 

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