C-Alkylation of Cyclic Enol Ether Mediated and Catalyzed by Lewis Acids

• Main Authors: Yen-wei chin, 閻維治
• Other Authors: Liang wmliang
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/gn2aj4

碩士 === 靜宜大學 === 應用化學研究所 === 94 === Reaction of cyclic enol ethers such as 2,3-dihydrofuran(DHF) and 3,4-dihydro-2H-pyran(DHP) with a variety of -dicarbonyls 2.1 such as 2,4-pentanedione(acetylacetone) 2.1a, ethyl acetoacetate 2.1b, 1-phenyl- 1,3-butanedione(benzoylacetone) 2.1c, 1,3-diphenyl-1,3-propanedione (dibenzoylmethane) 2.1d, 1,3-cyclohexanedione 2.1e, 5,5-dimethyl-1,3- cyclohexanedione(dimedone) 2.1f, and 4-hydroxycoumarin 2.1g mediated by using one equivalent of trifluoroacetic acid(TFA)-NaI afforded a series of C-tetrahydrofuranyl(C-THF) and C-tetrahydropyranyl (C-THP) products in high yields, respectively. Likewise, reaction of DHP and DHP with various phenols 2.4 such as phenol 2.4a, 2-methyl-phenol 2.4b, 1-naphthol 2.4c, and 2-naphthol 2.4d also obtained a series of ortho-directing substituted C-tetrahydrofuranyl (C-THF) products 2.5 and C-tetrahydropyranyl(C-THP) products 2.6 in high yields, respectively. When silica gel was participated in the reaction as a solid supporting material, the C-alkylation was also proceeding completely by using 0.1 equivalent of TFA only. . The proposed mechanism is that after the formation of oxonium intermediate from DHF or DHP the enol form of -dicarbonyls was proceeding the nucleophilic addition. Experimental results demonstrated that the reactivity of DHF is higher than DHP. In addition, the order of the reactivity for -dicarbonyls is parallel to the ratio of its enol form; i.e. cyclic -diketone > acyclic -diketone > -keto ester > > -diester. For the obtained products containing the cyclic -diketone substitute, the formation of thermodynamic stable intramolecular hydrogen bonding was resulted from the interaction between the hydroxyl group and the oxygen atom at the ring of THF or THP.