Antimony compounds, cyclization

Examples of cyclophosphazenes with ring systems containing elements other than phosphorus or nitrogen continue to be reported. The linear phosphazene [Ph2(H2N)Pi N.i P(NH2)Ph2]+Cl is cyclized by antimony pentachloride to give the compound (35). This result contrasts with... 

Oki and his co-workers (177) also found that these halogenated compounds (107) exhibited enormous differences in reactivity when they were treated with Lewis acids. The sc form undergoes a Friedel-Crafts type cyclization in the presence of titanium tetrachloride, which is a weak Lewis acid, whereas the ap form survives these conditions. The latter reacts in the presence of the stronger Lewis acid antimony pentachloride. This difference is apparently caused by a chloro group in proximity to the site where a cationic center develops during the reaction (Scheme 12). 

The only known example is hexahydro-lH-arsolo[l,2-a]arsole (17) (63JCS725). This unusual compound is prepared when the arsonium bromide (18) is heated to 200 °C (equation 6). Cyclization is accompanied by loss of methyl bromide to give (17 b.p. 100-102 °C/17 mmHg) which was characterized as the red palladium dibromide adduct (m.p. 150 °C). No analogous derivatives of antimony or bismuth have been reported. 

A -Alkylation. 2i/-l,3-Benzothiazine derivatives, a group of compounds with significant pharmacological activities, are synthesized by 7V-alkylation followed by cyclization of aryl and alkyl nitriles using antimony(V) chloride as a Lewis acid (eq 6). ... 

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