Abstract
(7S, 14S, 16R)- dialkyl 6-oxo-6,7,13,14-tetrahydro-7,14-methanobenzo[d]chromeno[3,4- h][1,6,3]oxathiazo-nine-14,16-dicarboxylates 4 and (S)-methyl 2-(2-methoxy-2-oxoethyl)-2,3- dihydrobenzo[d]thiazole-2-carboxylates 5 were readily synthesized in a ratio 3:1 and moderated yield by multicomponent reactions of 4-hydroxycoumarin and acetylenic esters with benzothiazole without using a catalyst. Also, The GIAO/DFT approach at the B3LYP/6-31G** level of theory was used to calculate the 1H, 15N, 17O and 13C NMR chemical shifts of product 4b. These computations are performed on the basis of X-ray structural data which are collected at 120(2) K temperature. In order to take into account intermolecular hydrogen bonds and the van der Waals effects, two different sizes of clusters (two model of trimeric and pentameric clusters) have been considered. A comparison between the experimental (Exp.) and calculated (Cal.) 1H and 13C NMR chemical shifts may reveal that the solution contains monomer, trimer1, trimer2, and pentamer models.
Keywords: Multicomponent reactions, chromeno[3, 4-h][1, 6, 3]oxathiazonine, dihydrobenzo[d]thiazole, benzothiazole, hydrogen bond, DFT study.
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