Dimerization of Cyclopentadienones

2,3,4,5-Tetraphenylcyclopenta-2,4-dien-1-one and 5,6,7,8-tetrachloro-3a,9a-dihydro-2,3,3a,9a-tetraphenylcyclopenta[2,3-b][1,4]benzodioxin-1-one–toluene (2/1): compounds of photochemical interest

“…Compound (I) was prepared by the method of Allen & Van Allan (1950) and recrystallized from ethyl acetate as dark-purple plates (0.42 × 0.30 × 0.07 mm). After preliminary oscillation and Weissenberg photographs, data were collected by equiinclination Weissenberg photographs (20ma x = 155 °) for layers 0-18 kl and h 0-1 I of the diagonal cell in space group 12/a and reindexed to the standard setting, C2/c ( -29 _< h ___ 24; 0 ___ k _< 9; 0 ___ l ___ 24).…”

Organic reactions in liquid crystalline solvents. 2. An investigation into the use of liquid crystalline solvents to effect stereochemical control in the Diels–Alder reaction

“…96-112°C (24)). Addition of 0.8 wt% 1 (as the Diels-Alder dimer (25)) results in a 3.5" depression in the optically-detected cholesteric-isotropic transition temperature of this compound. A similar depression (3") is observed in the smectic-nematic transition temperature of 4-ethyl-4'-(4-pentylcyclohexy1)-biphenyl (EPCB) upon addition of 0.4 wt% 1.…”

“…Addition of 0.4 wt% 1 has no discernible effect on the nematic-isotropic transition temperature of this compound. The ~i e l s -~l d e r dimer of 1 is known to be largely dissociated at 80°C (25). The reactions of 1 with 2a-d were carried out in benzene, cholesteryl nonanoate (ChN, isotropic), and ChP (cholesteric), at 105°C.…”

Structure of 2(5)-alkyl-4-hydroxy-3,4-diphenylcyclopent-2-en-1-ones, cyclocondensation products of benzil with aliphatic ketones

“…Other aliphatic ketones reacted with benzil to give cyclopentenones with alkyl groups on C 2 and C 5 . If the initial ketone is unsymmetrical, the condensation could give rise to four isomeric products [5]. If R ≠ H, three isomers I-III are obtained.…”

“…When the reactions of benzil with pentan-2-one and heptan-2-one were carried out in dilute solution, only one isomer I (R = Et, Bu) was obtained [5]. Under analogous conditions, octan-2-one (R = C 5 H 11 ) and 4-methylpentan-2-one (R = i-Pr) gave rise to mixtures in which three isomers I-III can be distinguished by 1 H NMR.…”