3-exo,3′-exo-(1R,1′R)-Bithiocamphor — a versatile source for functionally different 3,3′-bibornane derivatives — I. Ring-closure reactions and prototropic rearrangements

Photochemistry of Thiarubrine A and Other 1,2-Dithiins: Formation of 2,6-Dithiabicyclo[3.1.0]hex-3-enes

“…While cZt - 3b was twisted ca. 40° out of plane, tZt - 3b (not shown) was found to be planar; no energy minimum was found corresponding to cZc - 3b in either planar or twisted geometries. 6a,15a The frequencies and intensities calculated for the cZt - 3b geometry fit the experiments nicely 15a. An energy minimum was found for 9 in a slightly twisted s-cis geometry.…”

“…The quantum yield for conversion of 3,6-diphenyl-1,2-dithiin ( 1c ) to 2,5-diphenylthiophene ( 2c ) is 0.91 4d ring opening of 1 to ( Z )-butenedithione derivatives ( 3 ) has been postulated, 2ab,6a and involvement of various valence isomers of 3 in the desulfurization process has been suggested. 6b-d As well, direct extrusion of singlet sulfur from 1b is calculated to be disfavored by ca. 80 kcal mol -1 6a. Exposure of 1a to visible light, leading to desulfurization, results in enhanced biological activity …”

“…Electrocyclic ring opening followed by limited rotation about the C1−C2 bond could lead directly to cZt - 3b . Rotation in the opposite direction would afford cZc - 3b , disfavored relative to cZt - 3b . 2b,6a Compound cZt - 3b can then undergo either a 1,5-sigmatropic shift 13a, giving 9 or a π 4 a + π 2 a rearrangement giving 4b . Formation of 9 is apparently favored at 25 K in the Ar matrix.…”

High Pressure Effects on Zwitterionic and Thione Mesomeric Contributions in 2-Benzimidazole-2-Thione

“…The bond length changes in BzImS are of about this order of magnitudes, and these changes are compatible with the work energy of about 12 kJ mol –1 performed by the pressure of 2.0 GPa on the BzImS crystal. Our inspection of the CS bond in structures deposited in the Cambridge Crystallographic Database (CSD) shows clearly that they can be divided into compounds where the thione group is located in moieties of saturated C–C bonds, for example C sp 3 –C­(S)–C sp 3 , − and a group where the thione bond is conjugated. − The effect of the zwitterionic contribution for the CS bond length is clearly observed in the crystal structure of 1,3-dibenzyl-2-(4′,4′-dimethyl-2′,6′-dithioxocyclohexylidene) hexahydropyrimidine (refcode LEVRIN), where CS distances become 1.667 and 1.641 Å . On the other hand, according to a survey of the CSD, the average length of double bond CS is 1.681 Å, nearly exactly as this in BzImS at 0.1 MPa and considerably longer than that in CS 2 – 1.546(1) Å at 5.3 K/0.1 MPa and 1.550(2) Å at 295 K /3.7 GPa .…”

Monoterpenoids

“…514 Some ring-closure and prototropic rearrangement reactions of 374 have been studied. 515 Irradiation of 374 at 254 nm has been found to give 378. 516 The ligands 379 have been synthesised and catalyse the enantioselective addition of diethylzinc to benzaldehyde to give (S)-1-phenylpropanol of 85-88% ee.…”