Enantioselective Synthesis of a New Non-Natural Gabosine.

The preparation of a new non-natural gabosine is reported, in which the chirality is transferred from the toluene's biotransformed metabolite (1R,2S)-3-methylcyclohexa-3.5-diene-1,2-diol. Further chemical transformations to introduce additional functionality and chirality to the molecule were also accomplished.

General Method for the Synthesis of (-)-Conduritol C and Analogs from Chiral Cyclohexadienediol Scaffolds.

An efficient and facile general method for the synthesis of conduritol C analogs, taking advantage of an enantioselective biocatalysis process of monosubstituted benzenes, is described. The absolute stereochemical patterns of the target molecules (−)-conduritol C, (−)-bromo-conduritol C, and (−)-methyl-conduritol C were achieved by means of chemoenzymatic methods. The stereochemistry present at the homochiral cyclohexadiene-cis-1,2-diols derived from the arene biotransformation and the enantioselective ring opening of a non-isolated vinylepoxide derivative permitted the absolute configuration of the carbon bearing the hydroxyl groups at the target molecules to be established. All three conduritols and two intermediates were crystallized, and their structures were confirmed by X-ray diffraction. The three conduritols and intermediates were isostructural. The versatility of our methodology is noteworthy to expand the preparation of conduritol C analogs starting from toluene dioxygenase (TDO) monosubstituted arene substrates.

Crystal structure and absolute configuration of (4S,5R,6S)-4,5,6-trihy-droxy-3-methyl-cyclo-hex-2-enone (gabosine H).

The mol-ecule of the title keto carbasugar, C7H10O4, is formed by a cyclo-hexene skeleton with an envelope conformation, substituted by carbonyl, methyl and hydroxyl groups. The crystal structure is controlled mainly by a combination of strong O-H⋯O and weak C-H⋯O hydrogen bonds, forming nearly perpendicular chains running parallel to the [110] and [-110] directions. This perpendicularity is caused by a tetra-gonal pseudosymmetry influenced by the similarity between the a and b axes, the value of 90.9770 (10)° of the ß angle and the action of a 21 screw axis, which transform each chain into its corresponding nearly orthogonal one.

Crystal structure and absolute configuration of (3aR,3'aR,7aS,7'aS)-2,2,2',2'-tetra-methyl-3a,6,7,7a,3'a,6',7',7'a-octa-hydro-4,4'-bi[1,3-benzodioxol-yl], obtained from a Pd-catalyzed homocoupling reaction.

The absolute configuration, i.e. (3aR,3'aR,7aS,7'aS), of the title compound, C18H26O4, synthesized via a palladium-catalyzed homocoupling reaction, was determined on the basis of the synthetic pathway and was confirmed by X-ray diffraction. The homocoupled mol-ecule is formed by two chemically identical moieties built up from two five- and six-membered fused rings. The supra-molecular assembly is controlled mainly by C-H⋯O inter-actions that lead to the formation of hydrogen-bonded chains of mol-ecules along the [001] direction, while weak dipolar inter-actions and van der Waals forces hold the chains together in the crystal structure.

Crystal structure and absolute configuration of (3aS,4S,5R,7aR)-2,2,7-trimethyl-3a,4,5,7a-tetra-hydro-1,3-benzodioxole-4,5-diol.

The absolute configuration of the title compound, C10H16O4, determined as 3aS,4S,5R,7aR on the basis of the synthetic pathway, was confirmed by X-ray diffraction. The mol-ecule contains a five- and a six-membered ring that adopt twisted and envelope conformations, respectively. The dihedral angle between the mean planes of the rings is 76.80 (11)° as a result of their cis-fusion. In the crystal, mol-ecules are linked by two pairs of O-H⋯O hydrogen bonds, forming chains along [010]. These chains are further connected by weaker C-H⋯O inter-actions along [100], creating (001) sheets that inter-act only by weak van der Waals forces.

Electron Transfer Catalyzed [2 + 2] Cycloreversion of Benzene Dimers.

The catalysis of the [2 + 2] cycloreversion of the anti-o,o'-benzene dimer 1 and the syn-o,o'-naphthalene-benzene dimer 2 through thermal and photoinduced electron transfer is studied using experimental and computational methods. The reaction of the radical cations formed by electron transfer is at least 10(5) times faster than the thermal background reaction. It is demonstrated that the photoinduced electron transfer catalyzed reaction proceeds via an electron transfer sensitized pathway and that the observed inverse secondary deuterium isotope effect of 0.91 +/- 0.02 on the reaction is due to the equilibrium isotope effect on the electron transfer step. The relevance of these findings on the mechanism of the electron transfer catalyzed [2 + 2] cycloreversion of the biologically important cis,syn-cyclobutane-thymine dimer is also discussed.