3,3-Dimethylbicyclo[2.2.2]octa-5,7-dien-2-one (1). Electrolysis of the Diels-Adler adduct of 6,6-dimethylcyclo-hexadienone13 and maleic anhydride by using the procedure reported by Luibrand and Fujinari12 resulted in the bicyclic ketone 1: UV max (95% C2H2OH) 212 nm (e 3700), 230 (sh, 832), 297 (40). Deuterium-labeled ketone 412 was prepared by exchange of hydrogens of the adduct by using deuterium oxide and sodium deuterioxide heated to 150 °C for 24 h in a stainless-steel bomb calorimeter, prior to the electrolysis. The deuterium analysis17 of the resulting dicarboxylic acid is as follows: caled for exchange of two hydrogens, 16.67% excess deuterium; found, 13.17%, corresponding to 79% incorporation of two deuterium atoms. of 3,3-Dimethylbicyclo[2.2.2]octa-5,7dien-2-one (1). A solution of 0.63 mg of ketone 1 in 5 mL of ether in a quartz tube was irradiated with a 450-W, Hanovia, medium-pressure lamp fitted with a Vycor filter. GLC (FFAP) analysis after 75 min revealed that most of the starting material had reacted, and only peaks at very short retention times were present.
Direct IrradiationNone of the tricyclic ketone 6 formed.Photorearrangement of 3,3-Dimethylbicyclo[2.2.2]octa-5,7-dien-2-one (1). A solution of 0.49 g (3.3 mmol) of 3,3-dimethylbicyclo[2.2.2]octadien-2-one in 36 mL of acetone was placed in a quartz tube and degassed by bubbling nitrogen through the solution for 1 h. The tube was irradiated at room temperature with a 450-W, Hanovia, medium-pressure lamp fitted with a Vycor filter. Aliquots were analyzed by GLC (FFAP or di-n-decyl phthalate) and indicated the formation of a number of peaks with short retention times (one of which corresponded to the retention time of benzene), a primary photoproduct (6), and an unidentified product which formed upon continued irradiation of 6. GLC retention times (di-n-decyl phthalate, 0.64 cm X 3 m, 120 °C, He flow rate 60 mL/min) were as follows: starting ketone 1, 35 min; unidentified secondary photoproduct, 33 min; tricyclic ketone 6, 59 min. (A control experiment in which pure 6 was irradiated under the same conditions confirmed that the unidentified product was formed from 6.) After 16 h of irradiation, the solution was concentrated, and the products were isolated by preparative GLC (FFAP, 0.96 cm X 6 m, 150 °C, He flow rate 250 mL/min). Some starting ketone 1 (6.3 mg, retention time 43 min) was recovered, in addition to 48 mg (10%) of 4,4-dimethyltricyclo[3.3.0.02,8]oct-6-en-3-one (6, retention time 106 min) as a colorless liquid: IR (neat) 3030 (w), 2940 (m), 2905 (m), 1620 (s, carbonyl), 1590 (w), 1465 (m), 1376 (m), 1359 (m), 1342 (m), 1299 (m), 1087 (m), 893 (m), 747 (m) cm"1; NMR, see text and structure 6 for results; mass spectrum, m/e 148, 133, 70, 42; UV max (95% C2H6OH) 202 nm (e 7300), 233 (sh, t 1500). Anal. Caled for C10H12O: C, 81.04; , 8.16.Found: C, 80.82; H, 7.94. Purification of deuterated 6 from irradiation of 4 was carried out using a di-n-decyl phthalate GLC column. NMR results are shown in Table I.
