Stereoselective total synthesis of furofuran lignans through dianion aldol condensation

Highly stereoselective total synthesis of (+)-eudesmin, (+)-yangambin, (−)-eudesmin, and (−)-yangambin is described. This method is useful to generate the core skeleton of furofuran rings utilizing modification of Evans asymmetric aldol condensation.     

A pseudo multi-component electrochemical synthesis of spiro dihydrofuran derivatives

An electrochemical strategy to the assembly of tricyclic spiro dihydrofuran scaffold via the reaction of aryl aldehyde and dimedone has been developed successfully. This protocol has the advantages of high yields, wide application scope and an environmental benign procedure compared with the reported methods.     

A versatile stereoselective synthesis of endo,exo-furofuranones: application to the enantioselective synthesis of furofuran lignans

A new stereoselective route to endo,exo-2,6-diarylfurofuranones has been developed using Mn(III)-mediated intramolecular cyclopropanation and C-H insertion reactions as key C-C bond-forming steps. Mn(III)-mediated oxidative cyclization of acetoacetate derivative 11 afforded 1-acetyl-4-aryl-3-oxabicyclo[3.1.0]hexan-2-one (12) with excellent diastereocontrol (d.r. 22:1). Subsequent Lewis acid-catalyzed opening of the activated cyclopropane ring present in 12 with benzylic alcohols then gave alpha-acetyl-gamma-butyrolactones 16 and 18-20, which reacted efficiently with in situ-generated TfN(3) to secure the key alpha-diazo-gamma-butyrolactones 22-25. Highly stereoselective rhodium-catalyzed C-H insertion reactions of diazolactones 22-25 completed the synthesis of endo,exo-2,6-diarylfurofuranones 26-29 in overall yields ranging from 41 to 48% from 1-phenylallyl alcohol (+/-)-10. The approach developed for the furofuranones 26-29 was then applied to the asymmetric syntheses of four furofuran lignans, (+)-xanthoxylol (1), (+)-methylxanthoxylol (2), (+)-epipinoresinol (3), and (+)-epieudesmin (4), starting from enantiomerically enriched 1-arylallyl alcohol (S)-31.     

Dual template approach for the synthesis of hierarchically mesocellular carbon foams

We demonstrated a simple and effective dual-templating approach for the synthesis of hierarchically mesocellular carbon foams by using nonionic surfactant of sorbitan monooleate and silica colloid particles as sacrificial templates, and resorcinol/ formaldehyde as carbon source. The representative carbon foam has dual mesopore sizes of 4 and 10 nm, and possesses the specific surface area of 580 m2/g and the total pore volume of 0.80 cm3/g.     

An organic template approach for the synthesis of selectively functionalised tetraazacycloalkanes

Selectively functionalised tetraazacycloalkanes are obtained from the open-chain tetraamine by using a bisaminal moiety acting both as a template agent and as a N-protecting group.     

The carbenoid approach to peptide synthesis

A different approach to the synthesis of dipeptides is described based on the formation of the NHCHR1CONH-CHR2CO bond by carbenoid N-H insertion, rather than the formation of the peptide bond itself. Thus decomposition of triethyl diazophosphonoacetate catalysed by rhodium(II) acetate in the presence of N-protected amino acid amides 8 gives the phosphonates 9. Subsequent Wadsworth-Emmons reaction of 9 with aldehydes in the presence of DBU gives dehydro dipeptides 10. The reaction has been extended to a simple two-step procedure, without the isolation of the intermediate phosphonate, for conversion of a range of amino acid amides 11 into dehydro dipeptides 12 and to an N-methylamide 11 h, and for conversion of a dipeptide to tripeptide (13-->14). Direct conversion, by using methyl diazophenylacetate, of amino acid amides to phenylglycine-containing dipeptides 19 proceeds in good chemical yield, but with poor diastereoselectivity.     

The SYNGEN approach to synthesis design

In a systematic approach to the synthesis tree, the SYNGEN program first finds all convergent assembly plans for the target skeleton, i.e., all possible bondsets with no more than six bonds cut, from actual starting material skeletons. For each of these it then generates all possible sequential construction routes from real starting materials. These are “ideal syntheses”, the shortest synthetic routes. The output is displayed in graphics format with a flexible variety of modes for pruning to find the optimal choices in terms of real chemistry, with an interface to reaction databases (REACCS, SYNLIB) to locate literature precedents.     

Direct synthesis of uniform hollow carbon spheres by a self-assembly template approach

Hollow carbon spheres (50-100 nm) have been synthesized by a self-assembly approach using hexachlorobenzene and Na. NaCl which generated during the reaction has been successfully exploited as a template for the direct synthesis of porous carbon materials, which can be subsequently removed from carbon product by annealing above 1400 degrees C.     

Layer-by-layer nanotube template synthesis

Electroless deposition of gold on the pore walls of polycarbonate templates is currently the best known method for controlling inside diameters of template-synthesized nanotubes. It would be very useful to have alternative template-based synthetic chemistries that yield nanotubes composed of other materials, but which still allow for precise control over the nanotube wall thickness and i.d. A film-formation process that is based on layer-by-layer deposition of the film-forming material along the pore walls of the template membrane provides this desired alternative synthetic chemistry. We describe here the use of Mallouk's alpha,omega-diorganophosphonate/Zr layer-by-layer film-forming method for preparing nanotubes within the pores of alumina template membranes. We have found that this method allows accurate, quantitative, and predictable control over the wall thickness, and thus i.d., of the layered nanotubes obtained.     

Solution-phase template approach for the synthesis of Cu(2)S nanoribbons

In this paper, we have developed a solution-phase template approach to synthesize Cu(2)S nanoribbons for the first time. Bi(2)S(3) nanoribbons act as both template and reactant when treated with small CuCl particles, generating Cu(2)S nanoribbons with the assistance of the solvent ethanol. Nanoribbons with different compositions of Bi(2)S(3) and Cu(2)S also could be obtained through controlling the reaction time. This kind of template method is expected to be a general template approach due to its slow reaction rate and simplicity.     

The LILITH approach to organic synthesis planning

The general basis of the LILITH program is outlined. The size of the possible solution space is reduced by enhancing convergence, simplification and ordering. Complexity distance, relevant bond sets and ordering for bond-forming sequences are described. The evaluation of reactivity is the second main aspect in organic synthesis planning. Properties involving the ground state (native bond polarity) and the excited state (group-similar interference) contribute to the prediction of reactivity.     

A facile synthesis of the 20-hydroxyecdysone side chain via a dihydrofuran derivative

Key steps of a new synthesis of the 20-hydroxyecdysone side chain are (i) addition of 2 to 20-ketopregnanes and (ii) the stereoselective reduction of the 22-keto group after OH group protection.     

An efficient asymmetric synthesis of furofuran lignans: (+)-sesamin and (−)-sesamin

An efficient synthesis of (+)-sesamin 1a and (−)-sesamin 1b is described. The key reactions include highly stereoselective aldol condensation of piperonal 7 with the dianion of chiral oxazolidinone 8, followed by intramolecular ring cyclization of aldol product 11 in high yield.     

The approach to the synthesis of novel amino-C-glycosides

Stereoselective 1,3-dipolar cycloadditions of exo-glycals 1 to nitrones 2, 5 and 8 were investigated under the catalysis of Lewis acid or in a refluxing benzene or toluene solution, and afforded the corresponding cycloadducts of ketosyl spiro-isoxazolidines. The reductive cleavage of the N-O bond in the isoxazolidine ring and debenzylation by the catalytic hydrogenation [Pd(OH)₂/C] were approached using the glucose-type cycloadducts 6b and 6e to alkyl-C-glycoside derivatives 12, providing a new access to a novel alkyl-C-glycoside containing an amino group on the side alkyl chain.     

Gel template leaching: An approach to functional nanoporous membranes

A novel preparation method for nanoporous structures, denoted “Gel Template Leaching”, is described. The approach is based on the gelation of solutions containing two low molecular weight compounds of which one is crystallizable and the other curable. Gelation of the solute upon cooling followed by curing of the solvent below the gelation temperature lead to the formation of a semi-IPN consisting of a reversibly and a covalently crosslinked network. After leaching of the solute (the template) a well-defined nanoporous architecture was formed. Functional pores could be obtained after charging the pore walls with ionic sites.     

Pd-catalyzed sequential reaction for the synthesis of fused tricyclic compounds containing a dihydrofuran or isobenzofuranone unit

A novel Pd-catalyzed sequential reaction for the synthesis of fused tricyclic compounds with a dihydrofuran or isobenzofur-anone unit was developed.     

The template synthesis of mesoporous silicas with the thiourea functional group

Mono- and bifunctional mesoporous silicas containing the thiourea group ≡Si(CH₂)₃NHC(S)NHC₂H₅ or thiourea and various nitrogen-containing groups [≡Si(CH₂)₃NH₂, ≡Si(CH₂)₃NH(CH₂)₂NH₂, or {≡Si(CH₂)₃}₂NH], respectively, in the surface layer were prepared by template syntheses with cetylpyridinium chloride as a template. The synthesized samples had well-developed porous structures (S _sp = 750–1150 m²/g, V _c = 0.51–0.72 cm³/g, and d = 2.4–3.5 nm) and high functional group contents (1.0–2.0 mmol/g). Hydrothermal treatment of the mesophases in a mother liquor at 80°C (24 h) improved the structure-adsorption characteristics of the functionalized mesoporous silicas.     

Photoinduced template synthesis of cyclobutane-containing crown ether

The photoinitiated [2+2]-cycloaddition of 1,5-bis[2-(3-phenyl-3-oxoprop-1-en-1-yl)phenoxy]-3-oxapentane in solution was studied. In the presence of potassium cations, the reaction is intramolecular and gives crown ether containing the γ-truxin-type cyclobutane fragment (anti, head-to-head) as the major product. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 204–206, January, 2008.