Synthesis of Cyclic Enol Ethers from Alkenyl-β-dicarbonyl Compounds

Abstract

In this work we describe the cyclofunctionalization of eleven differently substituted alkenyl-beta-dicarbonyl compounds, employing three electrophilic reagents, namely, iodine, p-methoxyphenyltellurium trichloride, and phenylselenenyl bromide. The reactions occur through the enolic form of the substrates, to afford the corresponding iodo-, telluro-, or selenocyclic enol ethers. Substrates bearing trisubstituted double bonds failed in reacting with the selenium and tellurium reagents. In general, beta-diketones reacted faster than beta-keto esters with the three studied electrophiles.

Alcohol Substitution and Dehydrogenation of Selenium Compounds: A Convenient Preparation of Trisubstituted Furans from allyl-substituted 1,3-dicarbonyls

“…Compounds 3 were prepared as previously described. 32 Typical procedure for the preparation of 5-methoxymethyl-2methylfuran-3-carboxylic acid methyl ester (4a): To a solution of selenocyclic enol ether 3a (1 mmol) in dry DMF (5 ml) was added ammonium persulfate (2 mmol) and methanol (1 ml). The mixture was stired at 60°C for 3 h. Ethyl acetate (5 ml) and water (5 ml) were added and the water layer was separated and extracted with ethyl acetate (5 ml × 3).…”

“…29 Organoselenium reagent-induced electrophilic cyclisation of allyl substituted 1,3-dicarbonyl compounds can also proceed under rather mild and neutral conditions. 32 However, only 5-methyl substituted furans can be obtained by the classic deselenenylation with H 2 O 2 and DBU. 33 Here, an efficient preparation method of trisubstituted furans is reported by organoselenium reagent-induced electrophilic cyclisation of allyl substituted 1,3-dicarbonyl compounds, followed by alcohol substitution, accompanied with a dehydrogenation reaction of selenocyclic enol ethers, using ammonium persulfate and alcohol.…”

Molecular Iodine-Mediated Cyclization of Tethered Heteroatom-Containing Alkenyl or Alkynyl Systems

“…The 2-iodomethyl-3,5,6,7-tetrahydrobenzofuran-4-ones have also been recently prepared by polymer-supported selenium-induced electrophilic cyclization of allyl substituted 1,3-dicarbonyl compounds followed by cleavage of the selenium linkers using CH 3 I/NaI in DMF [ 24 ]. In another development, Ferraz and coworkers applied I 2 –NaHCO 3 mixture in dichloromethane at room temperature to series of α-alkenyl β-keto esters and γ-alkenyl β-keto esters bearing mono or disubstituted double bond to afford variously substituted iodocyclic ethers [ 54 ] Among the systems employed as substrates were the 2-allyl-1,3-cyclohexanedione derivatives 70 , which afforded 2-iodomethyl-3,5,6,7-tetrahydrobenzofuran-4-ones 71 in high yield ( Scheme 27 ) [ 54 ].…”

Preparações e aplicações sintéticas recentes de enaminonas

“…Nosso grupo de pesquisa, nos últimos anos, tem utilizado a ciclofuncionalização para obtenção de heterociclos oxigenados 38,39 e nitrogenados 40,41 . Em recente trabalho 42 , aplicamos a iodociclofuncionalização em β-enamino ésteres para obtenção de tetraidropiridinas que, após reação de desidroiodação, forneceram ciclopentanos trissubstituídos (Esquema 18).…”