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■ Trifunctionalized Allenes. Part VI. Synthesis of 2,5-Dihydro-1,2-oxaphospholes, Furan-2(5H)-ones and 5,6-Dihydro-2H-pyrans by Electrophilic Cyclization and Cycloisomerization of 4-Phosphorylated 6-Hydroxyhepta-2,3-dienoates

Ismail E. Ismailov, Ivaylo K. Ivanov, and Valerij Ch. Christov*

*Department of Chemistry, Faculty of Natural Sciences, Konstantin Preslavsky University of Shumen, 115, Universitetska str. BG-9712 Shumen, Bulgaria

Abstract

We have synthesized model compounds of three types heterocyclic compounds by electrophilic cyclization and cycloisomerization of 4-phosphorylated 6-hydroxyhepta-2,3-dienoates. Reactions with electrophiles produce mixtures of the 2,5-dihydro-1,2-oxaphosphole-5-carboxylates and the 5-phosphorylfuran-2(5H)-ones by competitive electrophilic cyclization due to the neighboring phosphonate (phosphine oxide) and the carboxylate groups participation. Starting compounds were smoothly converted into the corresponding 4-phosphoryl-5,6-dihydro-2H-pyran-2-carboxylates, by using 5 mol% of a silver salt as a catalyst in the 6-endo-trig cycloisomerization reaction.