First asymmetric total synthesis of (+)-steganacin determination of absolute stereochemistry

(+)-Steganacin was synthesized in a new and highly specific asymmetric pathway based on the novel application of chiral γ-lactone as a chiral synthon. By this synthesis the absolute stereochemistry of natural (?)-steganacin could be determined in unequivocal way.     

Diaminothiazoles and diaminothiophenes

Several 2,4-diaminothiazoles and 2,4-diaminothiophenes could be easily obtained by metallation using LDA from aminomethylthiomethylenecyanamides $\text{2}$ and aminomethylthiomethylenemalononitrile, respectively.     

The catalytic hydrogenolysis of 1-phenylbicyclo[4.1.0]heptane and the corresponding azidirine and epoxide

The hydrogenolysisof 1-phenylbicyclo[4.1.0]heptane (1a), cis-1-phenyl-2-methylbicyclo[4.1.0]heptane (1b), 1-phenyl-7-azabicyclo[4.1.0]heptane (2) and 1-phenyl-7-oxabicyclo[4.1.0]heptane (3) was studied using Ni, Pd, Rh and Pt as catalysts. The hydrogenolysis of the C₁C₇ bond of 1a and 1b led to the selective formation of trans-1-phenyl-2-methylcyclohexane (4a) with retention of configuration. Compound 1a gave not only 4a but also phenylcycloheptane (6a), which is the product of C₁C₆ bond fission, and the ratio of 6a to 4a increased in the sequence: Ni ? Pd, Rh < Pt. No C₁C₆ bond fission was observed in the hydrogenolysis of 1b. These results can be explained by a mechanism involving the formation of the π-benzyl complex.trans-2-Phenylcyclohexylamine (8) was obtained stereoselectively in the hydrogenolysis of 2 over Raney Ni. This selective formation can be ascribed to the competition of “SN i” and “radical” processes. The Pd catalysed hydrogenolysis gave cis-2-phenylcyclohexylamine (9) as the main product, while the presence of sodium hydroxide promoted the formation of 8.Raney Ni catalysed hydrogenolysis of 3 yielded a mixture of phenylcyclohexane (13) and 2-phenylcyclohexanols (10 and 11). trans-2-Phenylcyclohexanol (10) was the dominant isomer; the hydrogenolysis resulted in the predominant configurational retention. Compound 13 was confirmed to be produced via 1-phenylcyclohexene (12). This deoxygenation may be explained by a mechanism involving the radical cleavage reaction of 3. The presence of sodium hydroxide led to the formation of cis-2-phenylcyclohexanol (11). The Pd catalysed hydrogenolysis also gave mainly 11.The difference in behaviour of cyclopropane, azidirine and epoxide we ascribe to the differences in the affinity for the catalyst and differences in the electronegativity between C, N and O atoms.     

Photocrosslinkable polyesters with conjugated double bonds: Reciprocity effect in laser recording

The reciprocity effect under intense illumination was studied with photocrosslinkable polyesters of p-phenylenebis(α-cyanobutadiene carboxylic acid) (I), m-phenylenebis(α-cyanobutadiene carboxylic acid) (II), and p-phenylenebis(acrylic acid) (III), with an argon ion laser as a light source. The reciprocal sensitivities of I, II, and III were 5.0, 1800, and > 10⁵ mJ/cm², respectively. II and III required sensitization to enhance their sensitivities to a level at which reciprocity effects could be measured. I obeyed the reciprocity law over a wide range of exposure times from seconds to microseconds. Both II′, a copolyester of II, and III showed a dramatic decrease of sensitivity in high-intensity/short-time exposure when sensitized by 9,10-phenanthraquinone and pyrylium salts.     

Thermally stable rigid π-allylnickel compounds, (π-CHRCR′CR2)Ni(PPhMe2)C6Cl5

The reaction of C₆Cl₅Ni(PPhMe₂)₂Cl with CHRCR′CH₂MgX (X = Br or Cl) yields π-allylnickel compounds, (π-CHRCR′CH₂)Ni(PPhMe₂)C₆Cl₅ (Ia, R = R′ = H; Ib, R = H, R′ = CH₃; Ic, R = CH₃, R′ = H), which are stable in the solid state below ca. 150°C and are fairly stable in solution in the absence of oxygen. The π-allyl group was found by PMR spectroscopy to be rigid even in the presence of an excess of PPhMe₂, P(OEt)₃ or P(OMe)₃.     

DIFFERENTIAL EFFECTS OF A DNA-SYNTHESIS MUTATION ON UV-INDUCED MUTATION YIELDS IN VEGETATIVE CELLS AND SPORES OF BACILLUS SUBTILIS

Abstract— The absorption and emission properties of the photochemically produced dipyrimidine adducts are analyzed at 300 and 77K. Those adducts which have a saturated C(5)—C(6) bond in the pyrimidin-2,4-dione (Pyr) ring and a pyrimidin-2-one (Pyo) ring behave spectroscopically as a substituted Pyo. However, those consisting of one Pyr and one Pyo moiety can be considered as bichromophoric molecules and their spectral properties can be understood in terms of the relative torsional angle between the two rings. The adduct with the most bulky substituents ortho to the torsional bond bears the largest torsional angle and exhibits relatively independent absorption and emission phenomenon. At the other extreme, those adducts with no substituents at this position exist as almost planar molecules and exhibit considerable overlap of absorption bands as well as room temperature fluorescence which, in certain cases, is characteristic of intramolecular exciplex interaction. Using inter-ring torsional angles of ortho-substituted biphenyl molecules as a basis for comparative calculation, quantitative estimates of the torsional angles in dipyrimidine adducts at 300K have been made.     

Differential calculus on the quantum superspace and deformation of phase space

We investigate non-commutative differential calculus on the supersymmetric version of quantum space in which quantum supergroups are realized. Multiparametric quantum deformation of the general linear super-group,GL _q(m|n), is studied and the explicit form for the \(\hat R - matrix\) is presented. We apply these results to the quantum phase-space construction ofOSp _q(2n|2m) and calculate their \(\hat R - matrices\) .     

Synthesis and reactions of optically pure cyclohexyl(o-methoxyphenyl)phosphine-borane and t-butyl-(o-methoxyphenyl)phosphine-borane

Cyclohexyl(o-methoxyphenyl)menthyloxyphosphineborane and t-butyl(o-methoxyphenyl)menthyloxyphosphine-borane were prepared from dichlorocyclohexylphosphine and t-butyldichlorophosphine by successive treatments with (−)-menthol, o-methoxyphenylmagnesium bromide, and borane-THF complex. The separated pure diastereomers of each of the compounds underwent reaction with lithium naphthalenide to afford optically pure cyclohexyl(o-methoxyphenyl)phosphine-borane and t-butyl(o-methoxyphenyl)phosphine-borane, respectively. These secondary phosphine-boranes reacted readily with various electrophiles in the presence of bases with virtually net retention of configuration. A new chiral phosphine ligand, (S,S)-1,2-bis[cyclohexyl(o-methoxyphenyl)phosphino]ethane was synthesized via the optically pure phosphine-boranes.