Gianluigi Casalone

Stereoselective oxazaborolidine–borane reduction of biphenyl alkyl diketones–lignin models: enantiopure dehydrodiapocynol derivatives

Abstract Asymmetric reduction of two conformationally flexible biphenyl alkyl diketones 9 and 10 with (R)-oxazaborolidine 3-borane system was successfully carried out and the corresponding biphenyl alcohols 11 and 12 were obtained in high yield and e.e. with predominance of the homochiral (S,S) dicarbinols. The absolute configuration of diastereopure dehydrodiapocynol derivative (S,S)-14 was assigned by crystallographic analysis which confirms the known stereochemical course of CBS-catalysed reduction of ketones and gives useful information on spatial arrangement.

Asymmetric induction by the (S)-1-phenylethyl group in intramolecular nitrile imine cycloadditions giving enantiopure 3,3a-dihydro-pyrazolo[1,5-a][1,4]benzodiazepine-4(6H)-ones

Abstract Stereoselective intramolecular cycloadditions of homochiral nitrile imines 5 are described as a fruitful source of enantiopure 3,3a-dihydro-pyrazolo[1,5-a][1,4]benzodiazepine-4(6H)-ones 6 and 7.

C2-Symmetric sulfur derivatives of 2,2′,3,3′-tetramethoxybiphenyl

Abstract A practical route to prepare dithioether, thiophene and thiophene S -dioxide derivatives of 2,2′,3,3′-tetramethoxy-1,1′-biphenyl 1 is described. Resolution of 6,6′-bis(methylthio)-3,3′-dimethoxy-[1,1′-biphenyl]-2,2′-diol 15 was achieved and its absolute configuration was assigned by X-ray analysis of the corresponding phosphorothioamidate diastereomer 18 .

Chiral nonracemic C2-symmetry biphenyls by desymmetrization of 6,6′,2,2′-tetramethoxy-1,1′-biphenyl

Abstract Regioselective bromination of the title biphenyl 1 at the 3 and 3′ positions and simultaneous desymmetrization of the biphenyl has been achieved. Metal–halide exchange at the 3,3′ positions facilitated the introduction of functional groups in good yield. Regioselective reduction was obtained by using (CH3)3SiI, L-Selectride and HI according to the functional groups on the biphenyls. Resolution of 6,6′,2,2′-tetramethoxy-3,3′-dimethyl-1,1′-biphenyl 3 was achieved by its conversion to the corresponding phosphorothioamidate diastereomers of the (S)-(−)-α-methylbenzylamine. The absolute configuration of (M)-(+)-3 was confirmed by X-ray analysis of the corresponding diastereomer.

6,6′-Dibromo-3,3′-dimethoxy-2,2′-dihydroxy-1,1′-biphenyl: preparation and resolution

Abstract A pratical route to prepare the title biphenyl 1 starting from 3,3′,2,2′-tetramethoxy-1,1′-biphenyl 2 is described. Resolution of 1 was achieved by its conversion into the corresponding diastereomeric menthyldicarbonate. The absolute configuration of ( P )-(+)- 1 was confirmed by X-ray analysis of the related diastereomer.

Three Protected Tetrapeptides

The structures of three protected tetrapeptides, containing the Boc-Gly-Gly-Phe-X-OMe chain, tert-butoxycarbonyl-glycy-glycl-phenylalanine-leucine methyl ester dihydrate, Boc-Gly-Gly-L-Phe-D-Leu-OMe, C25H38N4O7.2H2O, tert-butoxycarbonyl-glycy-glycl-phenylalanine-methionine methyl ester dihydrate, Boc-Gly-Gly-L-Phe-D-Met-OMe, C24H36N4O7S.2H2O and tert-butoxycarbonyl-glycy-glycl-phenylalanine-norleucine methyl ester dihydrate, Boc-Gly-Gly-D-Phe-L-Nle-OMe, C25H38N4O7.2H2O, are described. The three molecules have the same conformation on the tetrapeptide chain and display the same packing, consisting of couples of molecules linked head-to-tail by two hydrogen (N--H...O) bonds; other hydrogen bonds, also involving two water molecules of crystallization, link these couples together and give rise to a planar structure.

The diastereoisomers methyl 5-(S)-[2-(R)/(S)-methoxycarbonyl)-2,3,4,5-tetrahydropyrrol-1-ylcarbonyl]-1-(4-methylphenyl)-4,5-dihydropyrazole-3-carboxylate.

The title diastereoisomers, methyl 5-(S)-[2-(S)-methoxycarbonyl)-2,3,4,5-tetrahydropyrrol-1-ylcarbonyl]-1-(4-methylphenyl)-4,5-dihydropyrazole-3-carboxylate and methyl 5-(S)-[2-(R)-methoxycarbonyl)-2,3,4,5-tetrahydropyrrol-1-ylcarbonyl]-1-(4-methylphenyl)-4,5-dihydropyrazole-3-carboxylate, both C(19)H(23)N(3)O(5), have been studied in two crystalline forms. The first form, methyl 5-(S)-[2-(S)-methoxycarbonyl)-2,3,4,5-tetrahydropyrrol-1-ylcarbonyl]-1-(4-methylphenyl)-4,5-dihydropyrazole-3-carboxylate--methyl 5-(S)-[2-(R)-methoxycarbonyl)-2,3,4,5-tetrahydropyrrol-1-ylcarbonyl]-1-(4-methylphenyl)-4,5-dihydropyrazole-3-carboxylate (1/1), 2(S),5(S)-C(19)H(23)N(3)O(5) x 2(R),5(S)-C(19)H(23)N(3)O(5), contains both S,S and S,R isomers, while the second, methyl 5-(S)-[2-(S)-methoxycarbonyl)-2,3,4,5-tetrahydropyrrol-1-ylcarbonyl]-1-(4-methylphenyl)-4,5-dihydropyrazole-3-carboxylate, 2(S),5(S)-C(19)H(23)N(3)O(5), is the pure S,S isomer. The S,S isomers in the two structures show very similar geometries, the maximum difference being about 15 on one torsion angle. The differences between the S,S and S,R isomers, apart from those due to the inversion of one chiral centre, are more remarkable, and are partially due to a possible rotational disorder of the 2-(methoxycarbonyl)tetrahydropyrrole group.

Vapour phase oxidation of 2,6-lutidine to 2,6-pyridinedicarboxaldehyde. III: Kinetic study

Abstract The oxidation reaction of lutidine (LUT) was carried out at 390–450°C over V-Mo-oxide catalyst, in presence of excess steam. A much simplified, but still significant kinetic model was obtained, useful for the design of a pilot plant, in view of a possible practical development of the process. The apparent ΔEa for the main reactions of the model range from ca. 111 to ca. 198 kJ mol−1, except for the formation of the heterocyclic byproducts from the lutidine-mono- and di-carboxaldehydes, for which a ΔEa of only 54 kJ mol−1 was found. LUT seems to adsorb on the catalyst more strongly than the partially oxidised products (ΔHa ≊ 350 and ≊ 190 kJ mol−1, respectively).

Two 17-hydroxy-9(10→5)-abeo-estr-4-ene-3,10-diones

(5S,9S,17S)-17-Hydroxy-9(10-->5)-abeo-estr-4-ene-3,10-dione, C(18)H(26)O(3), (II), and (5R,9R,17S)-17-hydroxy-9(10-->5)-abeo-estr-4-ene-3,10-dione, C(18)H(26)O(3), (III), are equimolecular products of the Fe(II)-induced transposition of 10beta-hydroperoxy-17beta-hydroxyestr-4-en-3-one, (I). With respect to reagent molecules, the configuration at C9 is retained for (II) while it is inverted in (III). The conformations of the five- and six-membered rings are compared.