Bridged-ring Compounds Research Articles

Photocatalytic Dearomative Construction of Bridged-Ring Compounds

Photocatalytic Dearomative Construction of Bridged-Ring Compounds

Meta‐OTf‐Substituted Diaryliodonium Salts Enabled Diels‐Alder Cycloadditions of Furans via Aryne Intermediates**

AbstractArynes are highly reactive intermediates that may be trapped with arynophilic reagents. However, the generation of benzyne necessitates stringent reaction conditions. The cycloaddition reaction of traditional benzyne precursors including diaryliodonium salts with arynophiles under strongly basic conditions encounters the limitations in tolerance of labile functional groups. To overcome this issue, the modulation of diaryliodonium structures are considered by incorporation of specific groups for activation of vinical C−H bond, enabling the generation of aryne intermediates in cycloaddition reactions under mild conditions. In this study, we reported meta‐trifluoromethanesulfonate (OTf) substituted diaryliodonium salts as benzyne precursor, in which the activation of C−I bond and selectively deprotonation of neighboring C−H bond generate highly reactive aryne intermediates for cycloaddition reactions with furans. This approach offers a simple and efficient method for synthesizing bridged ring compounds under mild reaction conditions with good functional group tolerance.

A new type of δ-vinylvalerolactone for palladium-catalyzed cycloaddition: synthesis of nine-membered heterocycles.

In this paper, a new type of δ-vinylvalerolactone was designed and synthesized, and used as a new precursor in Pd-catalyzed [6+3] cycloaddition with azomethine imines, leading to nine-membered 1,2-dinitrogen-containing heterocycles in 77-98% yields with >20 : 1 d.r. These nine-membered ring-fused products were further transformed into unusual tetracyclic bridged-ring compounds without loss of the diastereoselectivities.

Site-Selective Reaction of Enaminones and Enamine Esters for the Synthesis of Novel Diverse Morphan Derivatives.

An efficient and concise protocol was developed for the synthesis of diverse morphan derivatives 5–7 by the Michael and aza-Michael reaction of different types of quinone monoketals 1 or quinone imine ketals 2 with enaminones or enamine esters 3 promoted by 1,8-diazabicyclo[5.4.0]undec-7-ene in acetone at reflux. Notably, when cyclic enaminone 4 was used as a substrate in the aza-Michael and 1,2-addition reactions with quinone monoketals 1, they gave another novel morphan 8. This method is suitable for parallel synthesis of bridged ring compounds. As a result, highly diverse morphan derivatives were easily and efficiently prepared by the Michael/aza-Michael or aza-Michael/1,2-addition reactions.

Theoretical analysis of intramolecular double-hydrogen transfer in bridged-ring compounds

Abstract Model calculations are reported on double-hydrogen and double-deuterium transfer rates in two bridged-ring molecules recently investigated by Mackenzie. [Tetrahedron Letters, 33 (1992) 5629]. The calculations indicate that, contrary to an earlier interpretation, the two atoms are transferred by asynchronous tunnelling, the observed activation energy being representative of the energy of the biradical intermediate rather than the barrier height.

Topological considerations subtly inherent in the formulation and subdivision of fused vs. bridged ring compounds

Topological considerations subtly inherent in the formulation and subdivision of fused vs. bridged ring compounds

Palladium(II) catalysed construction of tetrasubstituted carbon centres, and spiro and bridged-ring compounds from enamides of 2-lodobenzoic acids

Various N-vinyl- and N-allyl-amides of 2-iodobenzoic acid undergo catalytic cyclisation in the presence of tetraethylammonium chloride and a palladium acetate-based catalyst system to generate a range of synthetically useful structural features including tetrasubstituted carbon centres, and spiro- and bridged-ring compounds, and in which 5-exo-trig cyclisations are kinetically favoured.

Bridged Ring Compounds by Malonic Ester Synthesis

Bridged Ring Compounds by Malonic Ester Synthesis

Condensed cyclic and bridged-ring systems. Part III. Regioselectivity and stereoselectivity in the acid-catalysed cyclisations of substituted benzylcyclohexanols. Stereocontrolled synthesis of some gem-carboxy–methyl-substituted hexahydrofluorene and hexahydro-5,9-methanobenzocyclo-octene derivatives

Treatment of ethyl 2-benzyl-2-hydroxy-1,3-dimethylcyclohexanecarboxylate (8) with polyphosphoric acid produced either (±)-c-2-benzyl-1,3-dimethylcyclohexane-r-1,c-3-carbolactone (6) or a mixture from which (1RS,4aRS,9aRS)2,3,4,4a,9,9a-hexahydro-1,4a-dimethyl-1H-fluorene-1-carboxylic acid (5a) was isolated in a moderate yield, depending upon the reaction temperature. Whereas aluminium chloride-catalysed cyclisation of the lactone (6) resulted in the stereospecific formation of (5SR,8RS,9SR,11RS)-5,6,7,8,9,10-hexahydro-8,11-dimethyl-5,9-methanobenzocyclo-octene-8-carboxylic acid (9), the epimeric t-2-benzyl lactone (7) produced a mixture of the hexahydrofluorene acid (5a) and the epimeric (8SR)-hexahydromethanobenzocyclo-octene acid (12), in high yields. By a similar process (±)-methyl t-2-benzyl-t-3-hydroxy-1,3-dimethylcyclohexane-r-1-carboxylate (4) gave the acid (9) and a mixture of hexahydrofluorene ester (5b) and (8SR)-hexahydromethanobenzocyclo-octene (13). Structures and configurations of the bridged-ring compounds were determined from chemical and n.m.r. spectral studies. Ready alkaline hydrolysis of the tertiary ester group in (5SR,8RS,9SR,11SR)-methyl 5,6,7,8,9,10-hexahydro-8,11-dimethyl-10-oxo-5,9-methanobenzocyclo-octene-8-carboxylate (11), through intramolecular oxo-group participation, revealed the stereochemistry of the ester group. The observed differences in the nature of products in polyphosphoric acid-catalysed cyclisation of (8) and the behavioural differences shown by the diastereoisomeric lactones (6) and (7) and the hydroxy-ester (4) in aluminium chloride-induced cyclisations are rationalised on the basis of steric and stereoelectronic factors in the intermediate cations as well as the thermodynamic stability of the products under reversible reaction conditions.

Ring-substituted derivatives of 5,6,11,12-tetrahydrodibenzo[b,f][1,4]-diazocine

Ring-substituted derivatives of 5,6,11,12-tetrahydrodibenzo[b,f][1,4]diazocine (IIb) have been prepared by the interaction of substituted NN′-bis-p-tolylsulphonyl-o-phenylenediamines (Ib—e) and αα′-dibromo-o-xylene, and hydrolysis of the products (IIc—f). In general, hydrolysis gives either the free base (IIg—j) or a mixture of this and the 5-p-tolylsulphonyl derivative (IVa—c), depending on the reaction time. The free bases (IIg—i) reacted with paraformaldehyde and with 5-nitro-2-furaldehyde to give bridged-ring compounds (III).

Bridged ring compounds. XVI. Stereoselectivity in expoxidation of bicyclic anhydrides

Bridged ring compounds. XVI. Stereoselectivity in expoxidation of bicyclic anhydrides

Electron-impact fragmentation of polychlorinated bridged-ring systems

Mass spectrographic analysis of a number of polychlorinated bridged-ring compounds based on the norbornene skeleton is described. The compounds examined have been grouped into classes according to their behaviour. Retro-Diels–Alder reactions (RDA), bond switching followed by 1,2-elimination, bridge scission with concomitant chlorine loss, stepwise chlorine elimination, and sigmatropic hydrogen transfer are processes which could be envisaged to account for the fragmentations observed.

Bridged ring compounds. VIII. 1-Halobicyclo[2.2.-2]octanes

Bridged ring compounds. VIII. 1-Halobicyclo[2.2.-2]octanes

Bridged Ring Compounds. X.1,2 The Reaction of Benzenesulfonyl Azide with Norbornadiene, Dicyclopentadiene, and Bicyclo[2.2.2]-2-octene

Bridged Ring Compounds. X.^1,2 The Reaction of Benzenesulfonyl Azide with Norbornadiene, Dicyclopentadiene, and Bicyclo[2.2.2]-2-octene

Parachor and Ring Structure. Part II. The Spatial Configuration of Bridged-ring Compounds.

Parachor and Ring Structure. Part II. The Spatial Configuration of Bridged-ring Compounds.