M. Gallego, M. Sierra
2004
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Abstract
The cyclization of E, E-dibenzylidenesuccinate esters to dihydronaphthalenes has been employed as the key step in the synthesis of lignans, a class of natural products found in plants. The stereochemistry of the cyclization products depends on the reaction conditions. For example, irradiation of succinate 1 in EtOH yields almost exclusively cis-dihydronaphthalene 2, whereas heating of 1 with trifluoromethanesulfonic acid (CF3SO3H, triflic acid) in CH2Cl2 yields trans-dihydronaphthalene 3 together with a small amount of the dearylized product 4. Prolonged heating or the use of excess triflic acid decreases the yield of 3, making compound 4 the major reaction product (Scheme 14.1).