An efficient synthesis of 4,5-dihydronaphtho[2,1-b]furan through a novel ring transformation of 2H-pyran-2-one

An innovative route for the synthesis of substituted naphtho[2,1-b]furan has been delineated through a ring transformation reaction of suitably functionalized 2H-pyran-2-ones by reaction with 6,7-dihydro-5H-benzofuran-4-one, in good yield.     

An innovative synthesis of dibenzofurans through a carbanion-induced ring transformation reaction

An innovative route for the synthesis of substituted dibenzofurans has been delineated through a ring transformation reaction of suitably functionalized 2H-pyran-2-ones by reaction with 7-methoxybenzofuran-3-one, in high yield. The novelty of the procedure lies in the creation of an aromatic ring from a 2H-pyran-2-one involving the -COCH₂-moiety of the substrate.     

An efficient synthesis of (E)-(2-arylpyrazino[1,2-a]pyrimidine-4-ylidene)acetonitriles and cyanomethyl appended pyrimidines

A series of (E)-(2-arylpyrazino[1,2-a]pyrimidine-4-ylidene)acetonitriles 5a-j and aryl/heteroaryl tethered pyrimidin-4-yl acetonitriles 6a-e has been synthesized in excellent yields through base catalyzed ring transformation of suitably functionalized 2H-pyran-2-ones 3 using 2-aminopyrazine 4a and arylamidinium salts 4b, separately.     

A novel route for the synthesis of highly congested aryl-tethered 2-aminobenzylamines through ring transformation of 2-pyranones

An innovative and efficient synthesis of highly congested 2-amino-3-aminomethyl-5-methylsulfanyl/sec-aminobiphenyl-4-carbonitriles 4 has been delineated through base catalyzed ring transformation of 6-aryl-4-methylsulfanyl/sec-amino-2H-pyran-2-one-3-carbonitriles 1 with Boc-protected 1,3-diamino-2-propanone 2, followed by TFA catalyzed hydrolysis of the intermediate [3-tert-butoxycarbonylaminomethyl-4-cyano-5-methylsulfanyl/sec-aminobiphenyl-2-yl]carbamic acid tert-butyl ester 3 in moderate yields as the TFA salts.     

Understanding the acceleration in the ring-opening of lactones delivered by microwave heating

This paper reports the first detailed study focussed upon identifying the influence that microwave heating (MWH) has upon the mechanic steps involved in the tin catalysed ring-opening of lactones such as ?-caprolactone (CL). Direct comparison of conventional (CH) and microwave (MWH) heated kinetic studies showed that a key factor in the reduction of the polymerisation cycle time with MWH was the elimination of the induction period associated with in situ catalyst manufacture and initiation. NMR studies demonstrated that the most significant mechanistic change contributing to the observed induction time reduction/elimination was faster initiation (i.e., reaction of the initiatior/catalyst complex with the first monomer unit). Consequently, analysis of the dielectric properties of the reaction components predicted that this MWH induced change was related to the selective volumetric heating of both the catalyst and the monomer. Furthermore, this indication of the greater significance of the initiation step in defining the length of the induction period suggests that this is the rate determining step of the process, whether conducted by CH or MWH. Increasing the catalyst concentration was demonstrated to produce significant reductions in reaction heat-up time and to induce a significant (up to 30 °C) overshoot in reaction mixture bulk temperature in with MWH only. Thus supporting the conclusion that selective heating of the organometallic species in the system contributes directly to differences in the reaction conditions and which need to be taken into account when drawing comparisons with CH systems. Consequently, both effects were concluded to be thermally generated from selective volumetric heating.     

Silica‐Bound 3‐{2‐[Poly(ethylene Glycol)]ethyl}‐Substituted 1‐Methyl‐1H‐imidazol‐3‐ium Bromide: A Recoverable Phase‐Transfer Catalyst for Smooth and Regioselective Conversion of Oxiranes to β‐Hydroxynitriles in Water

A series of β‐hydroxynitriles were efficiently synthesized from the regioselective ring opening of oxiranes by cyanide anion in the presence of silica‐bound 3‐{2‐[poly(ethylene glycol)]ethyl}‐substituted 1‐methyl‐1H‐imidazol‐3‐ium bromide (SiO₂? PEG? ImBr) as a novel recoverable phase‐transfer catalyst in H₂O (Scheme 1 and Table 2). The workup procedure was straightforward, and the catalyst could be reused over four times with almost no loss of catalytic activity and selectivity.     

新型2-氧代-1,2,4-三唑并[3,2-d][1,5]苯并氧氮杂类稠杂环的合成

将取代色满酮(1)与芳肼反应生成的腙与HNCO发生[3+2]环加成反应,加成产物(2)经氧化得到偕偶氮异氰酸酯(3).化合物3在HBF4的催化下发生环化-重排反应,得到新颖的三环系2-氧代-1,2,4-三唑并[3,2-d][1,5]苯并氧氮杂化合物5a～5g.     

Properties of a Ring Critical Pointas Measures of Intramolecular H-Bond Strength

Summary.  The topological parameters derived from the Bader theory such as the electron density and its Laplacian at the ring critical point (RCP) are analysed here as possible measures of the H-bond stength for intramolecular H-bonds. The parameters of RCP correlate well with the other properties of intramolecular H-bonds which are known as good measures of the H-bond strength. The calculations were performed on two samples of compounds with intramolecular H-bonds: the derivatives of malonaldehyde and the derivatives of o-hydroxybenzaldehyde. MP2 and HF calculations were carried out using a 6-311++G^** basis set. E-mail: slagra@krysia.uni.lodz.pl Received February 18, 2002; accepted (revised) May 27, 2002     

Extremely facile ring inversion and rearrangement in fluorobicyclo[2.1.0]pentanes

cis-1,2,3,4,5,5-Hexafluorobicyclo[2.1.0]pentane and 1,2,4,5-tetrafluorobicyclo[2.1.0]pentane have been synthesized from hexafluorobenzene. The former hydrofluorocarbon, which exists entirely in the endo configuration, rearranges to cis-1,2,3,3,4,5-hexafluorocyclopentene below room temperature (E_a = 21.9 kcal/mol, log A = 13.4). The latter undergoes degenerate ring inversion with extraordinary ease (ΔG^‡ = 6.8 ± 0.2 kcal/mol at −55 °C). Density functional calculations indicate that significant bonding between the bridgehead carbons is retained in the ring inversion transition state. Analogous calculations predict for hexafluorobicyclo[1.1.0]butane a considerably lower barrier for ring inversion and more 1,3-bonding in the transition state.     

Synthesis and conformational analysis of naphth[1′,2′:5,6][1,3]oxazino[3,2-c][1,3]benzoxazine and naphth[1′,2′:5,6][1,3]oxazino[3,4-c][1,3]benzoxazine derivatives

A new functional group, the hydroxy group, was inserted into a Betti base by reaction with salicylaldehyde, and the naphthoxazine derivatives thus obtained were converted by ring-closure reactions with formaldehyde, acetaldehyde, propionaldehyde or phosgene to the corresponding naphth[1′2′:5,6][1,3]oxazino[3,2-c][1,3]benzoxazine derivatives. Further, the conformational analysis of these polycyclic compounds by NMR spectroscopy and an accompanying molecular modelling are reported; especially, both quantitative anisotropic ring current effects of the aromatic moieties in these compounds and steric substituent effects were employed to determine the stereochemistry of the naphthoxazinobenzoxazine derivatives.