On the preparation of azepinones

We report here a simple and efficient preparation of 1H-azepin-5(2H)-ones and their unexpectedly facile isomerization to 1H-azepin-5(4H)-ones under mildly basic reaction conditions.     

An efficient synthesis of 2-alkylpyridines using an alkylation/double decarboxylation strategy

We have discovered a novel route for synthesising 2-alkylpyridines by exploiting the decarboxylation of pyridyl malonate esters. Herein we report the synthesis of a number of examples and describe how the reaction was discovered.     

Chemoenzymatic Synthesis of Cylindrocyclophanes A and F and Merocyclophanes A and D

Incorporating enzymatic reactions into natural product synthesis can significantly improve synthetic efficiency and selectivity. In contrast to the increasing applications of biocatalytic functional-group interconversions, the use of enzymatic C−C bond formation reactions in natural product synthesis is underexplored. Herein, we report a concise and efficient approach for the synthesis of [7.7]paracyclophane natural products, a family of polyketides with diverse biological activities. By using enzymatic Friedel–Crafts alkylation, cylindrocyclophanes A and F and merocyclophanes A and D were synthesized in six to eight steps in the longest linear sequence. This study demonstrates the power of combining enzymatic reactions with contemporary synthetic methodologies and provides opportunities for the structure–activity relationship studies of [7.7]paracyclophane natural products.     

Reactions of 1,4-bis(tetrazole)benzenes: formation of long chain alkyl halides

The reactions of 1,4-bis[2-(tributylstannyl)tetrazol-5-yl]benzene with α,ω-dibromoalkanes were carried out in order to synthesise pendant alkyl halide derivatives of the parent bis-tetrazole. This led to the formation of several alkyl halide derivatives, substituted variously at N1 or N2 on the tetrazole ring. The crystal structures of 1,4-bis[(2-(4-bromobutyl)tetrazol-5-yl)]benzene (2-N,2-N′), 1,4-bis[(2-(4-bromobutyl)tetrazol-5-yl)]benzene (1-N,2-N′) and 1,4-bis[(2-(8-bromooctyl)tetrazol-5-yl)]benzene (2-N,2-N′) are reported. Further discussion involves the structure of 1,4-bis[2-(6-bromohexyl)-2H-tetrazol-5-yl]benzene (2-N,2-N′) previously reported.     

A facile and convenient method for synthesis of alkyl thiocyanates under homogeneous phase transfer catalyst conditions

A simple and environmentally friendly method is described for the efficient conversion of alkyl halide to alkyl thiocyanate using tetrabutylammonium bromide （TBAB） as a phase transfer catalyst. The reactions occur in water and furnish the corresponding alkyl thiocyanate in high yields. No evidence for the formation of isothiocyanates as by-product of the reaction was observed and the products were obtained in pure form without further purification.     

Reactions of polychlorophenyllithium compounds with electrophiles

Polychloroaromatic compounds lithiated by BuⁿLi in THF react with several electrophilic agents of which aldehydes and epoxides seem to be the most promising from the preparative point of view. Dedicated to Corresponding Member of the Russian Academy of Sciences E. P. Serebryakov on the occasion of his 70th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 941–946, April, 2005.     

Reactions of oxalyl fluoride with electrophiles

The reactions of oxalyl fluoride with electrophiles in the presence of alkali metal fluoride were carried out. In the reaction with CF₃CH₂OTf (Tf=CF₃SO₂) or CH₃CH₂OTf, the synthesis of di-ether (ROCF₂CF₂OR) and mono-ether (ROCF₂COF) was achieved. The difference of the reactivities between these two compounds was discussed from the result of DFT calculations.     

Reactions of activated aryl sydnones with electrophiles

Electrophilic substitution on the aryl or sydnone ring of some ortho-substituted activated N-aryl-sydnones is reported.     

Synthesis of cananodine by intramolecular epoxide opening

Cananodine is a guaipyridine alkaloid with activity against liver cancer. Cananodine was synthesized using a remarkable intramolecular opening of a trisubstituted epoxide as the key step in construction of the seven-membered carbocycle of the target. The epoxide opening strategy allows all four stereoisomers of cananodine to be prepared.     

Further Investigation on the Rearrangement Mechanism of Reactions of 1,5-Benzothiazepines with Ethoxycarbonylcarbene

IntroductionDuring the last decade,our group has investigateda series of cycloaddition reactions of2,3-dihydro-1,5-benzothiazepines withα-carbonyl-ketenes[1,2],nitrileoxides[3,4],nitrile imines[3,4],ketenes[5—8],andcarbenes[9—11].Normal cycloadducts ca…     

Reactions of lithiated 2,5-dimethylazaferrocene with selected electrophiles

Lithiation of 2,5-dimethylazaferrocene 1 with sec-BuLi/TMEDA in THF at −78 °C proceeds (as shown by quenching with D₂O) to comparable extent on the methyl groups and the Cp ring. However, the outcome of the reaction of the lithiated 1 with an electrophile depends on the nature of this electrophile. In the reaction with 4-methoxybenzaldehyde only the product originated from the lateral lithiation is formed, whereas the reaction with 4-methoxyacetophenone and 4,4′-dimethoxybenzophenone afforded mixtures of the products resulting from lateral and ring-lithiation. Similar results were also obtained in the reaction of lithiated 1 with chlorodiphenylphosphine and diphenyl diselenide. On the other hand, the exclusive formation of the Cp-substituted product was observed in the reaction of lithiated 1 with N,N-dimethylformamide. The structures of selected products (oily compounds were transformed into the corresponding crystalline W(CO)₅-complexes) were confirmed by X-ray diffraction. The presented reactions open a novel entry to specifically substituted azaferrocenes (especially those containing heteroatom substituents) with potential applications as ligands for the homogenous catalysis.     

Reactions of 3-azido-1,2,4-triazole with electrophiles

Alkylation of 3-azido-1,2,4-triazole with oxiranes, bromoacetone, and methyl vinyl ketone furnished a mixture of N-substituted 3- and 5-azido-1,2,4-triazoles, 3-azido compounds prevailing. The same substrate subjected to heterylation with 3,5-dinitro-1,2,4-triazole derivatives reacted selectively at the N¹ atom, and its bromination afforded 3-azido-5-bromo-1,2,4-triazole..Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 11, 2004, pp. 1699–1704.Original Russian Text Copyright © 2004 by Kofman, Krasnov.     

Construction of bicyclic systems containing an oxygen bridge by isomerization of cyclic epoxy alcohols

A novel method for constructing a 7-oxabicyclo[2.2.1]heptane skeleton was developed. The substrates, namely cis-3,4-epoxy-1-cyclohexanol derivatives, were prepared from the corresponding 3-cyclohexen-1-ol derivatives via a stereoselective epoxidation reaction using a vanadium catalyst. Upon heating with lithium iodide in propionitrile, the cis-epoxy alcohol was transformed into the 7-oxabicyclo[2.2.1]heptane derivative in high yield. The reaction proceeds through formation of a lithium alkoxide bearing an iodohydrin moiety, followed by an intramolecular S_N2 reaction.     

Silver-catalyzed coupling reactions of alkyl halides with indenyllithiums

Coupling reactions of tertiary and secondary alkyl halides with indenyllithiums proceeded effectively in the presence of a catalytic amount of silver bromide to provide tertiary- and secondary-alkyl-substituted indene derivatives in good yields.     

Alkylation on graphite in the absence of Lewis acids

Graphite is introduced as a convenient catalyst for alkylation of aromatic compounds and alcohols by benzyl, tertiary alkyl, and secondary alkyl halides in the absence of strong Lewis acids. Primary alkyl halides are not active under the reaction conditions.     

Boron trifluoride-catalyzed reaction of alkyl fluoride with silyl enolate, allylsilane, and hydrosilane

Alkylation of silyl enolates with tert-alkyl or allylic fluorides proceeds smoothly in the presence of a catalytic amount of boron trifluoride to afford the corresponding carbonyl compounds. Allylation and reduction of alkyl fluorides with allylsilane and hydrosilane, respectively, occur under BF₃ catalysis.     

Reactions of 3,5-dimethyl-1-phenyl-1H-pyrazole with electrophiles

Reactions of 3,5-dimethyl-1-phenyl-1H-pyrazole with various electrophilic reagents were studied. Electrophilic attack occurred regioselectively at the C⁴ atom in the pyrazole ring.     

The first facile total synthesis of natural （3R,4R,6S）-3, 4-epoxybisabola- 7 （ 14 ）, 10-dien-2-one

3,4-Epoxybisabola-7(14),10-dien-2-one,a natural sesquiterpoind,was first synthesized from(-)-carvone through 7 steps,in an overall yield of 35.9%.The key step was the allylation and then a substrate-directable epoxidation was committed successfully.     

Intramolecular and Intermolecular Schmidt Reactions of Alkyl Azides with Aldehydes

Despite recent advances in the use of alkyl azides in ring expansion reactions of ketones, there has been little work done on the corresponding chemistry of aldehydes. In the present study, the Lewis acid-promoted reactions of alkyl azides with aldehydes were studied in both intermolecular and intramolecular contexts. The intramolecular reactions of azidoalkyl aldehydes in which the azide and carbonyl groups were separated by 2-5 carbons were examined. Although the examples having the shortest tether failed (3-azidopropanals), each of the other systems gave good yields of either NH-substituted lactams (resulting from hydride migration in the initially formed azidohydrin adduct) or formamides (alkyl migration). The product formed was dependent on the chain length of the starting azido aldehyde. The intermolecular reactions were less efficient, requiring TiCl₄ promotion for even moderate yields, and in each case gave mixtures of products resulting from hydride and alkyl migration.     

Indium-mediated cleavage of diphenyl diselenide and diphenyl disulfide: efficient one-pot synthesis of unsymmetrical diorganyl selenides, sulfides, and selenoesters

A convenient and efficient method was developed for the synthesis of alkyl phenyl selenides, sulfides, and selenoesters in one-pot reaction by using indium metal. The reaction showed the selectivity for tert-alkyl, benzylic, and allylic halides over primary and secondary alkyl halides. For the reaction of primary and secondary alkyl iodides and bromides, the yields of selenides were improved by the addition of a catalytic amount of iodine.