The alkylation of some representatives of β-dicarbonyl compounds by 1,4-dibromo-2-butene and ethyl 2,3-dibromopropionate was investigated.Furans represent one of the important classes of heteroaromatic compounds. Substituted furans are usually synthesized by the regioselective insertion of carbon substituents into furan or its acyclic precursors [1]. Universal and convenient synthons for the "construction" of furans and related heterocycles containing an acyl group at position 3 of the heterocycle are β-dicarbonyl compounds. In recent years [2-4] a series of reviews have been published on numerous methods for the synthesis of furans from 1,3-diketones, which are valuable intermediates in the synthesis of liquid crystals, various heterocycles, and physiologically active substances and particularly pheromones and prostaglandins [5][6][7][8].We investigated the alkylation of some representatives of β-dicarbonyl compounds by various dihalides in order to obtain functionally substituted dihydrofurans.While continuing study of the reactivity of β-dicarbonyl compounds [9, 10] we realized the reactions of dimedone, allyl acetoacetate, acetylacetone, and acetoacetic ester with ethyl 2,3-dibromopropionate (1) and 1,4-dibromo-2-butene (2) in the K 2 CO 3 -DMSO system. It was established that the alkylation of dimedone with compounds 1 (Scheme 1) and 2 (Scheme 2) takes place exclusively in the direction of C,O-cycloalkylation with the formation of 2-ethoxycarbonyl-6,6-dimethyl-2,3,4,5,6,7-hexahydrobenzo[b]furan-4-one (3) and 6,6-dimethyl-2-vinyl-2,3,4,5,6,7-hexahydrobenzo[b]furan-4-one (9) respectively.In the reaction of allyl acetoacetate with the ester 1 we obtained 4-allyloxycarbonyl-2-ethoxycarbonyl-5-methyl-2,3-dihydrofuran (4).

In the title moleclue, C16H13ClN2O2, the cyclo­hexene ring is in a sofa conformation. The pyran ring is essentialy planar [maximum deviation = 0.038 (2) Å] and forms a dihedral angle of 89.68 (10)° with the benzene ring. In the crystal, mol­ecules are linked by pairs of N—H⋯N hydrogen bonds, forming inversion dimers with R 2 2(12) ring motifs. These dimers are further linked by N—H⋯O hydrogen bonds into chains along [110]. Weak C—H⋯O hydrogen bonds are also present.

The title mol­ecule, C21H30N2O5, is chiral with four stereogenic centres. The crystal is a racemate and consists of enanti­omeric pairs with the relative configuration rac-(6S*,7R*,8R*,9S*). The ethyl fragment of the eth­oxy­carbonyl group at position 6 is disordered in a 0.46 (3):0.54 (3) ratio. The crystal structure features inter­molecular N—H⋯O. Intra­molecular O—H⋯N and N—H⋯O hydrogen bonds also occur.

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