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Substituted benzocyclobutenes were isolated from the reaction of substituted oxocycloocta-2,8-diene-1,2-dicarboxylates with DMAD which were themselves formed by the microwave assisted [2+2] cycloaddition of cyclic enaminones to dimethyl acetylenedicarboxylate. The high pressure hydrogenation of (1E,2Z)-dimethyl 3-(dimethylamino)-7-oxocycloocta-2,8-diene-1,2-dicarboxylate gave oxabicyclo[3.3.1]non-3-ene-2,3-dicarboxylates, while use of low pressure hydrogenation resulted in only the carbonyl group being reduced to give the corresponding hydroxyl derivative which was proposed as an intermediate of the oxabicyclo[3.3.1]nonanes formed using high pressure hydrogenation.

Reactions of cyclic enaminones, derived from cyclic five- and six-membered 1,3-diones, and dimethyl acetylenedicarboxylate (DMAD) under microwave irradiation produced a mixture of two products: ring-expansion products as a result of a [2+2] cycloaddition and Michael adducts. Reaction between 4-(dimethylamino)-2H-chromen-2-one and DMAD leads to three products: 2-(4-(dimethylamino)-2-oxo-2H-chromen-3-yl)maleate as a Michael adduct, dimethyl 1-(dimethylamino)naphthalene-2,3-dicarboxylate as the product of the [2+2] cycloaddition followed by 6π disrotatory electrocyclization and elimination of CO2 and 4-(dimethylamino)naphthalene-1,2-dicarboxylate as the product of the [4+2] cycloaddition followed by elimination of CO2.

A simple, metal-free method for the synthesis of the title pyridines is developed, which complements the existing methods of 2-pyridine synthesis by coupling reactions of organometallic reagents.

The lithiation of 2-bromophenyloxiranes (I) followed by a reaction with enaminones (II) leads to diastereomeric isochromanes (III) and (IV), which are readily separable by column chromatography.

Herein a simple, metal-free synthesis of 2-alkyl-, 2-cycloalkyl-, 2-aryl-, and 2-heteroaryl-substituted pyridine 3,4-dicarboxylates and their N-oxides from the corresponding methyl ketones in good to excellent yield, demonstrated with 22 examples in each case, is described. The method complements the current coupling reactions of 2-heterocyclic organometallic reagents.

Eleven (S)-1,6-dialkylpiperazine-2,5-diones and five (3S,6S)-1,3,6-trialkylpiperazine-2,5-diones were prepared in three steps from the corresponding (S)-α-amino acid esters comprising of reductive N-alkylation, N-acylation and cyclisation. The synthesis of (S)-1,6-dialkylpiperazine-2,5-diones has a broad scope allowing preparation of diketopiperazines with primary and secondary alkyl groups at N(1), while the synthesis of (3S,6S)-1,3,6-trialkylpiperazine-2,5-diones is limited to compounds with primary alkyl groups at N(1). Reductive alkylation of amino acid ester hydrochlorides by catalytic hydrogenation in the presence of a carbonyl compound proved to be a simple, efficient and general method for the preparation of stable (storable) α-alkylamino acid ester hydrochlorides. The structures of the novel compounds were determined by NMR and X-ray diffraction.

Substrates (I) undergo a microwave-promoted cycloaddition with DMAD to give cyclobutene intermediates which afford the desired functionalized 1,3-dienones after ring opening.