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Ring closure reactions O 0130 Synthesis of Hetero-and Carbocycles by Nucleophilic Substitution at sp 2 Carbon. -(MIYAUCHI, H.; CHIBA, S.; FUKAMIZU, K.; ANDO, K.; NARASAKA*, K.; Tetrahedron 63 (2007) 26, 5940-5953; Dep. Chem., Grad. Sch. Sci., Univ. Tokyo, Bunkyo, Tokyo 113, Japan; Eng.) -Bartels 41-033

The use of alkenyl acylphosphonate and acylphosphine oxide derivatives as acceptors in radical cyclizations was studied under thermal and photochemical conditions, respectively. The cyclizations of alkenyl acylphosphonates under thermal conditions occurred smoothly in refluxing dioxane using benzoyl peroxide as an initiator; the addition of diethyl phosphite increased the chemical yield. Photochemically induced cyclizations of alkenyl acyldiphenylphosphine oxides at 300 nm gave similar results, although a notable difference was observed in one case. The intramolecular cyclization of S-but-3-enyl phosphinothiolformates occurred under thermal and photochemical conditions, providing thiolactones, whereas S-pent-4-enyl phosphinothiolformate afforded the tetrahydrothiophene derivative under similar conditions.

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Organo-phosphorus compounds S 0080Radical Cyclizations of Alkenyl Acylphosphonate Derivatives under Thermal and Photochemical Conditions. -Cyclizations of alkenyl acylphosphonates (I), (III), and (VII) in the presence of a combination of benzoyl peroxide and diethyl phosphite occur smoothly under thermal conditions. The generated phosphonyl radical not only works as a radical carrier but also adds to the alkenyl moiety of the acylphosphonate. Similar results are obtained by photochemically induced cyclizations of alkenyl acyldiphenylphosphine oxides (IX), (XIII), and (XV). However, the intramolecular cyclization of butenyl phosphino thiolformate (XIII) yields the thiolactone (XIV), whereas the higher homologues of (XIII), (XI), afford the tetrahydrothiophene derivatives (XII), due to an intramolecular homolytic substitution at sulfur. -(CHO, C. H.; KIM*, S.; YAMANE, M.; MIYAUCHI, H.; NARASAKA, K.; Bull. Chem.