Synthesis of new compounds containing the 2,3-dihydro[1,4]dioxino[2,3-b]pyridine heterocyclic system as a substructure

2,3-Dihydro-spiro[1,4]dioxino[2,3-b]pyridine-3,3′-pyrrolidine (8A) and 2,3-dihydro-spiro[1,4]dioxino[2,3-b]pyridine-3,4′-piperidine (9A) have been synthesized from 2-chloro-3-pyridinol. The corresponding 2,3′ (8B) and 2,4′ (9B) isomers were obtained via the Smiles rearrangement, while 9B was also selectively synthesized from 2-nitro-3-pyridinol. The separation of the isomers A and B under the sulfamide form was carried out by flash column chromatography. Subsequent transformations of the corresponding dioxinopyridine derivatives were described.     

Facial selectivity of the Ireland-Claisen rearrangement of allylic esters of 2-methyl and 2-methoxycyclopentanecarboxylic acids

Ketene silylacetals derived from prenyl and (Z)- and (E)-crotyl 2-methylcyclopentanecarboxylates (9) were subjected to the Ireland-Claisen rearrangement. All three substrates rearranged with complete facial selectivity, but the (Z)- and (E)-crotyl systems gave a mixture comprised of the same diastereomers of 1-(1-methyl-2-propenyl)-2-methylcyclopentanecarboxylic acid (14) in ratios of 2:1 and 1:2, respectively. In contrast, the ketene silylacetals prepared from allyl and prenyl 2-methoxycyclopentanecarboxylates (22) underwent rearrangements with both facial stereochemistries.     

Cyclodextrin catalysis of the smiles rearrangement of 4-nitrophenyl salicylate

α- and β-Cyclodextrins accelerate the Smiles rearrangement of 4-nitrophenyl salicylate which proceeds through the mechanism of intramolecular aromatic nucleophilic substitution. The binding and catalytic rate constants were calculated from the dependences of the observed pseudo-first-order rate constants of the rearrangement reaction on cyclodextrin concentration obtained at various pH values. The catalysis was interpreted in terms of a tighter binding of the anionic, highly delocalized δ-complex intermediate than that of the substrate to cyclodextrins.     

分子CH_3NH=B:的结构及重排反应的理论研究

采用量子化学中的从头计算方法, 在MP2/6-31G(d,p)水平上研究了不饱和硼烯CH3NH=B:的结构及重排反应机理。结果表明, CH3NH=B:的单线态结构比三线态结构稳定, 该分子的基态是单线态。分子CH3NH=B:可以发生3种不同的重排反应。本文找到了这3种重排反应的过渡态, 并详细计算了不饱和硼烯CH3NH=B:重排反应的动力学函数, 据此讨论了不饱和硼烯CH3NH=B:的稳定性问题。     

Recyclization of Condensed Carbethoxypyrimidines Accompanied by Substitution of a Carbon Atom into the Heterocycle

Condensation in ethanol of ethyl ethoxymethyleneacetoacetate with systems containing an amidine fragment (substituted 3-aminopyrazoles and 3-amino-1,2,4-triazole) gave 6-carbethoxy-7-methylpyrazolo[1,5-a]pyrimidines. Addition of base to solutions of the obtained bicyclic carbethoxy derivatives in the course of several minutes caused rearrangement to 6-acetyl-7-hydroxypyrazolo[1,5-a]pyrimidine and 6-acetyl-7-hydroxy-1,2,4-triazolo[1,5-a]pyrimidine respectively. A more prolonged refluxing in 15% aqueous alcohol solution of base caused 6-carbethoxy-7-methyl-2-phenylpyrazolo[1,5-a]pyrimidine and 6-acetyl-7-hydroxy-2-phenylpyrazolo[1,5-a]pyrimidine to recyclize to 7-methylpyrazolo[1,5-a]pyrimidine.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 569–576, April, 2005.     

Synthesis and thermal cyclization of an enediyne-sulfonamide

The synthesis of an enediyne sulfonamide by alkylidene carbene rearrangement is reported. The compound cyclizes thermally to give the Bergman product, which was prepared independently for comparison. Like other σ-acceptor substituents at the enediyne alkyne termini, such as fluoride, oxonium or ammonium groups, the sulfonamide moiety enhances the reactivity for thermal Bergman cyclization as shown by the cyclization kinetic of the title compound.     

Biotransformation of two stemodane diterpenes by Mucor plumbeus

The microbiological transformation of 13α,17-dihydroxy-stemodane (2) by the fungus Mucor plumbeus afforded 13α,17,19-trihydroxy-stemodane (3), 3β,13α,17-trihydroxy-stemodane (5), 3-oxo-13α,17-dihydroxy-stemodane (7), 7α,13α,17,19-tetrahydroxy-stemodane (8), 3β,11α,13α,17-tetrahydroxy-stemodane (10), 3β,7α,13α,17-tetrahydroxy-stemodane (12), 3β,8β,13α,17-tetrahydroxy-stemodane (14), 2α,13α,17-trihydroxy-stemodane (16), 2α,13α,17,19-tetrahydroxy-stemodane (17), 2α,3β,13α,17-tetrahydroxy-stemodane (20) and 3β,11β,13α,17-tetrahydroxy-stemodane (22), whilst the incubation of 13α,14-dihydroxy-stemodane (25) gave 3β,13α,14-trihydroxy-stemodane (28), 2α,13α,14-trihydroxy-stemodane (29) and 13α,14,19-trihydroxy-stemodane (30). Preference for hydroxylations of ring A at C-2(α), C-3(β) and C-19 were observed in both incubations. An interesting rearrangement of 13α,14α-dihydroxy-stemodanes to 14-oxo derivatives with an unusual carbon framework has been observed under acetylation conditions. We have named this skeleton prestemodane, which, as a hydrocarbon ion, had been postulated as a biogenetic precursor of stemodane.     

Metal complexes with an aminosubstituted tricarbollide ligand

The reaction of the tricarbollide salt Tl[7-tBuNH-7,8,9-C₃B₈H₁₀] (Tl1) with [(cod)Rh(THF)_x]⁺ gives the rhodium complex [1-(cod)-12-tBuNH-1,2,4,12-RhC₃B₈H₁₀] in almost quantitative yield. Analogous reactions of Tl1 with [(ring)M(THF)_x]²⁺ ((ring)M = Cp*Rh and (1,3,5-C₆H₃Me₃)Ru) afford the corresponding metallatricarbollides [1-(ring)-12-tBuNH-1,2,4,12-MC₃B₈H₁₀] in ca. 50% yield. Refluxing Tl1 with [Mn(CO)₃(MeCN)₃]⁺ in THF give the tricarbollide analogue of cymantrene, [1,1,1-(CO)₃-12-tBuNH-1,2,4,12-MnC₃B₈H₁₀], the structure of which was determined by single-crystal X-ray diffraction analysis. In all cases, the formation of the metallatricarbollide complexes is accompanied by polyhedral rearrangement leading to the maximum separation of the cage carbon atoms.     

Synthesis of shikalkin and certain related compounds

A successful total synthesis of a biologically active pigment from plants of the Boraginaceae family was carried out with naphthazarine as the starting material, and using the 1,4,5,8-tetramethoxynaphthalene, the corresponding 2-vinyl derivative and its epoxide or a cyclopropane adduct with diazoacetic ester at the key stages. In the course of developing the scheme of the synthesis of shikalkin, its three analogs were obtained, differing in the nature of the monoterpenoid side chain.For preliminary report, see [1].Pacific Ocean Institute of Bioorganic Chemistry, Far East Branch of the Russian Academy of Sciences, 690022 Vladivostok. N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1901–1910, August, 1992.     

Synthesis of chiral [5]helicenes using aromatic oxy-Cope rearrangement as a key step

Both enantiomers of (P)-(+)-2- and (M)-(−)-2-acetoxy-11,14-dimethyl[5]helicenes 8 were synthesized by asymmetric aromatic oxy-Cope rearrangement of the corresponding chiral bridged bicyclic compounds, which were obtained by enzymatic resolution. The absolute configurations of 8 were assigned by their circular dichroism spectra.