Edward R. Cullen

Carbon-13 nuclear magnetic resonance studies of some organoselenium compounds containing carbon–selenium double bonds

Carbon-13 n.m.r. spectra were obtained for eight compounds having C = Se double bonds. These comprised five selenoketones, 2,2,4,4-tetramethylpentane-2-selone (1-Se), 1-thia-3,3,5,5-tetramethylcyclohexane-4-selone (2-Se), 1,1,3,3-tetra methylindane-2-selone (3-Se), 2,2,5,5-tetra methylcyclopent-3-ene-1-selone (4-Se), and selenofenchone (5-Se), one selenoester, ethyl selenobenzoate (6-Se), and two selenoamides, NN-dimethylselenobenzamide (7-Se) and NN-dimethyl-2,2-dimethylselenopropanamide (8-Se). Coupling constants, 1J(13C–77Se), were measured for (1) and (3)–(7). A comparison was made among the chemical shifts of (1)–(8), their oxygen analogues, and the sulphur analogues of (1), (5), and (7). The selenocarbonyl carbon atoms were shifted 34–72 p.p.m. downfield and the α-carbon atoms 10–19 p.p.m. downfield from their oxygen analogues. The differences, δΔSe, O, for the remaining carbons are only a few p.p.m. Values of 1J(13C–77Se) were 209–221 Hz, much larger than any previously observed 13C–77Se coupling constants.

“Tied-back” carbocyclic intermediates in the preparation of very sterically strained olefins: Derivatives of tetra-tert-butylethylene

Abstract The preparations of the extremely sterically hindered olefins (12) and-(13) are described, and attempts to convert these compounds to other derivatives of tetra- tert -butylethylene (1) are outlined.

Thermal and photochemical studies of symmetrical and unsymmetrical dihydro-1,3,4-selenadiazoles

The thermal and photochemical reactivities of very sterically hindered dihydroselenadiazoles were investigated. The symmetrical tied-back dihydroselenadiazoles (4)–(6), and unsymmetrical fenchane (1,3,3-trimethylnorbornane) derived dihydroselenadiazoles (10)–(12) proved to be relatively thermally stable and could be used as intermediates in the preparation of the symmetrical olefins (7)–(9) and fenchane-derived olefins (15)–(17). The di-t-butylmethylene-derived dihydroselenadiazoles (28)–(30) were isolable, but underwent complete retrocyclization on thermolysis. Photolysis of symmetrical and unsymmetrical dihydroselenadiazoles afforded the corresponding azines in good yield.