Synthesis of diesters by addition of acids to 5-alkoxycarbonylnorborn-2-ene and related 5-methyl derivatives

Abstract

The addition of saturated aliphatic acids C 1 -C 5 to 5-alkoxycarbonylnorborn-2-enes and 5-methyl-5-alkoxycarbonylnorborn-2-enes in the presence of catalyst BF 3 ·O(C 2 H 5 ) 2 was studied and new representatives of the norbornane hydroxyacids diesters were synthesized. Bicyclic diesters of diols and hydroxy acids are practically valuable organic compounds that have been successfully used in various fields as effective solvents [1], plasticizer for polymers [2], synthetic oils [3], and aroma substances [4].Due to the urgency of obtaining bicyclic diol diesters, we formerly carried out the addition of monocarboxylic saturated acids C 1 -C 6 and unsaturated acrylic and methacrylic acids to the acetoxy-and acetoxymethylnorbornene that resulted in the synthesis of the corresponding diesters, which can be used as fragrance compounds and monomers [5][6][7].In this paper we studied a reaction of catalytic addition of saturated monocarboxylic acids to 5-alkoxycarbonylnorborn-2-enes and related 5-methyl derivatives for the synthesis of new classes of bicyclic diesters.The studies showed that saturated monocarboxylic acids are regioselectively added in the presence of catalyst BF 3 ·O(C 2 H 5 ) 2 to alkoxycarbonylnorbornene to form the diesters, 2-acyloxy-5-alkoxycarbonylnorbornanes.To find the optimal conditions for the reaction of the diesters formation, we studied the effect of molar ratio of reacting components in the range 0.5-1.3:1 on the addition of acetic acid to 5-methoxycarbonylnorborn-2-ene as an example, at the temperature 50-90ºC, reaction duration 1.8 h, and amount of catalyst BF 3 ·O(C 2 H 5 ) 2 0.06-0.14 wt % to acetic acid. The results are shown in the figure.As seen from the data obtained, the optimal conditions of the formation of diester in the reaction of acetic acid with 5-methoxycarbonylnorborn-2-ene in the presence of boron trifluoride etherate are as follows: the molar ratio of 5-methoxycarbonylnorborn-2-ene to acetic acid 1:1.1, the amount of BF 3 ·O(C 2 H 5 ) 2 0.1 wt % to acetic acid, temperature 80ºC, duration 4 h. Under these conditions, the yield of 5-methoxycarbonylnorborn-2-yl acetate is 88.0%.The found optimum conditions were also implemented to the addition of other saturated monocarpboxylic acids: formic, propionic, butyric, isobutyric, and valeric. The yields of diesters depend on the structure of the monocarboxylic acid and decrease from 92.0 to 61.5% in the series from formic to valeric acid: I−IV R 1−2 R 2−3 OOC t, kt + R 1−6 COOH I−XXX R 1−2 R 2−3 OOC OCR 1−6 O X I V V−X