Formation mechanism of furfuryl sulfides from o-furfuryl dithiocarbonates: density functional theory study for aromatic [3,3]-sigmatropic rearrangement.

Density functional theory (DFT) calculations at the B3LYP/6-31G(d) and B3LYP/6-31G+(d) levels demonstrated that O-furfuryl S-alkyl dithiocarbonate (1) undergoes aromatic [3,3]-sigmatropic rearrangement to the energetically unfavorable S-(2-methylene-2,3-dihydrofuran-3-yl) S-alkyl dithiocarbonate (2'), which then rearranges to furfuryl alkyl sulfide (3) with COS extrusion to regain the aromaticity lost in the first step.

New formation mechanism of allylic trithiocarbonates from sodium O-(2-Alkenyl) dithiocarbonates via sequential pericyclic reactions: Density functional theory study.

Density functional theory (DFT) calculations at the B3LYP/6-31G(d) level demonstrated that sodium O-(3-phenylallyl) dithiocarbonate undergoes [3,3]-sigmatropic rearrangement to sodium S-(1-phenylallyl) dithiocarbonate, which then isomerizes to the more thermodynamically stable sodium S-(3-phenylallyl) dithiocarbonate. The calculations also showed that sodium 2-alkenyl trithiocarbonates and their esters are more labile towards the allylic rearrangement.

Chemical reactivity of dihydropyrazine derivatives. Cycloaddition behavior toward ketenes.

The cycloaddition behavior of dihydropyrazines toward ketenes was investigated using single-crystal X-ray structures of the cycloadducts and density functional theory (DFT) calculation data. The reaction proceeds via a stepwise pathway involving an orientation complex prior to formation of the betaine intermediate. This is followed by electrocyclization to afford the 1 : 1 and 1 : 2 adducts bearing beta-lactam ring(s).

Crystallographic evidence for cyclopropane ring formation in isotwistenes obtained by thermal cascade reactions of cyclopentadienone with acyclic conjugated dienes.

The molecular structure of the double Diels-Alder (DDA) adduct derived from three-step thermal cascade reactions of 2,5-bis(methoxycarbonyl)-3,4-diphenylcyclopentadienone with ethyl sorbate is elucidated by single crystal X-ray analysis. The structural features and the reaction mechanism of the adduct are discussed on the basis of density functional theory (DFT) calculation results.

New C(28) steroidal glycosides from Tubocapsicum anomalum.

Two new C(28) steroidal glycosides, tuboanosides A (1) and B (2), were isolated from the fruit of Tubocapsicum anomalum MAKINO. Their chemical structures were elucidated on the basis of spectroscopic and X-ray diffraction analysis of the p-bromobenzoyl derivative (4) of tuboanosigenin (3), the sapogenol derivative of these two glycosides. Tuboanosides have the structural peculiarity of an unusual side chain carrying an unusual linkage with a C-21 bound to C-25 on the lactone ring.

New C(28) steroidal glycosides from Tubocapsicum anomalum.

Three new C(28) steroidal glycosides, isotubocaposides A (1), B (2), and C (3), were isolated from the fruits of Tubocapsicum anomalum MAKINO. Their chemical structures were elucidated on the basis of spectroscopic and X-ray diffraction analysis of p-bromobenzoyl derivative (5) of isotubocaposigenin (4), the sapogenol derivative of these three glycosides. Isotubocaposides have the structural peculiarity of an unusual side chain carrying a C-21 bound to C-24 on the lactone ring.

NMR spectroscopic characterization of metoprolol/cyclodextrin complexes in aqueous solution: cavity size dependency.

The inclusion complex formation of a water-soluble beta(1)-selective adrenoreceptor antagonist Metoprolol (Met) with alpha-cyclodextrin (alpha-CyD), beta-cyclodextrin (beta-CyD), gamma-cyclodextrin (gamma-CyD), and 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) in aqueous solution was studied by ultraviolet (UV), circular dichroism (CD), and nuclear magnetic resonance (NMR) spectroscopies and the modes of interaction were assessed. Continuous variation plots revealed that Met forms the inclusion complexes with alpha-CyD, beta-CyD, and HP-beta-CyD in a stoichiometry of 1:1, whereas gamma-CyD forms the 2:1 complex where two Met molecules are included in one gamma-CyD cavity. NMR spectroscopic studies, including ROESY and GROESY techniques, clearly indicated that alpha-CyD with the small cavity includes the methoxyethylbenzene moiety of Met molecule shallowly in the cavity, depositing the benzene and the methoxy moieties around the secondary and primary sides, respectively, of the cavity. In the case of the beta-CyD complex, the methoxyethylbenzene moiety is more deeply included in the cavity, and it is feasible that Met may be able to enter from both primary and secondary hydroxyl sides of the cavity, forming the 1:1 complex. On the other hand, two Met molecules are included probably in an antiparallel orientation in the large gamma-CyD cavity, and the benzene moieties of Met are in contact with each other.

Pericyclic reaction of ketenes with cascade reaction products of pyridine N-oxides and dipolarophiles. X-ray structures of the adducts and formation mechanism.

The structures of the adducts derived from the reactions of substituted ketenes with dihydropyridine derivatives have been clarified by single crystal X-ray analyses and the formation mechanism is discussed on the basis of the reaction-path calculations by semiempirical and density functional theory (DFT) molecular orbital methods.

Carboxylic acid clathrate hosts of Diels-Alder adducts of phencyclone and 2-alkenoic acids. Role of bidentate C-H ... O hydrogen bonds between the phenanthrene and carbonyl groups in host-host networks.

Carboxylic acid host compounds (3) having a phenanthrene-condensed bicyclo[2.2.1]hept-2-en-7-one skeleton have been synthesized by the [4 + 2]pi cycloaddition of phencyclone (1a) with 2-alkenoic acids (2) and their inclusion behavior was investigated. The endo [4 + 2]pi cycloadducts (3) enclathrated alcohols and ethers besides aromatics and ketones. The X-ray crystallographic analysis of the inclusion compound (3ac-dioxane) of the endo [4 + 2]pi cycloadduct (3ac) of phencyclone and trans 2-butenoic acid (2c) indicated that dioxanes are located at the opposite side of the bridged carbonyl of the bicyclo[2.2.1]hept-2-en-7-one moiety, in which the O-H...O and C-H...O hydrogen bonds play an important role in the inclusion complex formation. Similarly, a pair of 3-pentanone molecules were included in the endo [4 + 2] pi cycloadduct (3ae) of 1a and cinnamic acid (2e). In both cases, the hosts are linked by the edge-to-face interaction between the phenanthrene and phenyl rings and the "bidentate" C-H...O hydrogen bonds between the phenanthrene-ring hydrogens and the bridged carbonyl or the carboxylic carbonyl group. The endo [4 + 2] pi cycloadduct (3bl) of tetracyclone (1b) and acrylamide (2l) also showed a wide-range inclusion behavior, in which alcohols are included by making a hydrogen-bond loop with the amide groups. The inclusion behavior of the carboxylic acid Diels-Alder hosts is discussed on the basis of the single crystal X-ray analysis, thermal analysis and semiempirical molecular orbital calculation data.

Atropisomers of 1-(acyl or aroyl)-2-naphthylindolines. Isolation, X-ray crystal structure and conformational analysis.

A series of pairs of stable diastereomeric atropisomers caused by restricted rotation around the Csp3-Csp2 bond of [2-(2-hydroxynaphthalen-1-yl)-3,3-dimethyl-2,3-dihydroindol-1-yl]-(3- or 4-substituted phenyl)-methanone or [2-(2-hydroxynaphthalen-1-yl)-3,3-dimethyl-2,3-dihydroindol-1-yl]-1-alkanone were isolated. The conformational analyses of the atropisomers were performed based on the X-ray crystallographic and (1)H-NMR spectral data. It became clear that rotation about the C2-naphthyl bond is restricted at room temperature, whereas the >NCO-Ar bond rotates freely.

Cascade reaction of imines with phenylsulfinylallene. X-ray structure of the product and its formation mechanism.

The structure of the product derived from the reaction of a dihydropyridine derivative with phenylsulfinylallene has been clarified by a single crystal X-ray analysis and the formation mechanism is discussed on the basis of the reaction-path calculations by semiempirical and ab initio molecular orbital methods.