Trihalides rings

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 structure of the complex (96) between benzaldehyde (95) and boron trifluoride (equation 15) was investigated by X-ray crystallography169. In 96, BF3 is in the anti position to the phenyl ring and this geometry remains also in solutions, as tested by the 19F-NMR spectrum in CD2CI2. An ab-initio study170 on interactions between formaldehyde and boron trihalides showed that these complexes (mainly donor-acceptor complexes) affect spectroscopic properties and the reactivity of the carbonyl group the polarization of the C=0 bond favours the attack of nucleophiles. 

Zyk et al. <2000RJ0794> reported the synthesis of fused-ring thietanes by the reaction of the bis-morpholine sulfide-phosphoryl trihalide complex 85 with norbornadiene. The formation of 4-thiatricyclo[3.2.1.03,6]octane 86 was demonstrated and yields varied slightly depending on the phosphoryl trihalide used. When phosphoryl trichloride was used, the yield was 69% in the case of phosphoryl tribromide, it was 72%. The complex 84 was obtained by the reaction of the bis-morpholine sulfide with phosphoryl trihalide in dichloromethane at —40°C (Scheme 15). The same authors <1996RCB2393> performed a similar reaction of norbornadiene with bis-morpholine disulfide-phos-phoryl tribromide complex 87, which led to the formation of the same thietane 86 in 63% yield (Scheme 15). These reactions have also been described by Robin and Rousseau in a review <2002EJ03099>. 

Alkyl groups from alkyl aryl telluriums that have a stabilizing nitrogen functionality in the aromatic ring in an orr/zo-position to the tellurium atom are cleaved by bromine, iodine or sulfurylchloride. Aryl tellurium halides or trihalides are produced in these reactions. 

Tris(cyclopentadienyl)lanthanide complexes with steri-cally more crowded Cp ligands such as C5Me4R (R = Me, Et, Tr, and SiMe3) are not assessable by simple metathesis between lanthanide trihalides and the respective alkali metal salt of the bulky Cp ligand. For instance, Cp 3Sm, obtainable from Cp 2Sm and cyclooctatetraene, reacts with THF with ring-opening forming Cp 2Sm[0(CH2)4Cp ](THF) (equation 14). 

A group of related zwitterionic (see Zwitterion) compounds is formed by the addition of lithium phosphinomethanides to either PnCb or P4, which result in four- or six-membered rings (equation 21). It should be noted that the attempted reduction of Sb and Bi trihalides to form - -1 oxidation state compounds typically results in the production of Sb° or Bi°, which precipitates from solution. ... 

In the case of 87e and 87f insertion of a second equivalent of phosphinidene complex [(CO)5W-PCH(TMS)2] into a P-C or P-P bond of the three-membered ring has led to l,2-dihydro-l,2,3 triphosphete complexes lOOe and lOOf. The reactions of aluminium trihalides and gallium trichloride with 3 equiv of kinetically stabilized phosphaalkynes P CR proceed according to an unusual spirocyclotrimerization to provide the complexes 103a-103f exhibiting structural features of a zwitterionic diphosphirenium alkanide complex (Scheme 37). 

Tri(organoseleno)boranes 35 are prepared from boron trihalides and organic selenolates as stable compounds (Scheme 35) [63]. These selenoboranes have been shown to be useful for the conversion of carbonyl compounds into seleno-acetals 36 [64] and the selective ring opening of epoxides [65]. Recently, it was reported that tri(phenylseleno)borane reacts with cyclic ethers to produce m-hydroxyalkyl phenyl selenides 37 in the presence of a catalytic amount of Lewis acid [43]. 

---