Aryltelluroformates as precursors of selenium-containing heterocycles

Benzylselenoalkyl-substituted telluroformates, synthesized according to the sequence depicted in the accompanying scheme, give different Se-containing heterocycles (depending from the length of the alkyl chain) by photolytic or thermal processes.  

Route (a) can be considered as the first example of intramolecular homolitic substitution at selenium, whereas route (b) must likely involve a nucleophilic attack by the selenium moiety with decarboxilative removal of phenyltellurolate. 

4-Octyl-3-oxaselenan-2-one A 0.15 M solution of l-(benzylseleno)-3-undecyl (phenyl-telluro)formate A (n = 2) (103 mg, 180 pmol) in benzene in a water-cooled jacket was irradiated with a 250 W low-pressure mercury lamp (white light) at a distance af 20 cm for 64 h. Removal of the solvent in vacuo and preparative TLC (hexane/ethyl acetate, 85 15) afforded the product B as a pale oil (37 mg, 73%). 

2-Octyltetrahydroselenophene was prepared using l-(benzylseleno)-4-dodecyl (phenyl-teUuro)formate A (n = 3) in benzene (0.46 M) with heating at 160°C for 2 days. Preparative TLC (hexane/ethyl acetate, 98 2) afforded the product C as a pale oil (87%). 

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