Chemistry of the Podocarpaceae. XLVIII. Photo-sensitized oxidations of unsaturated ring-c aromatic diterpenoids

Abstract

Photo-sensitized oxidation of the 6,7-dehydro ring-c aromatic diterpenoids (5), (8) and (38) affords high yields of the corresponding 5-ene-7-ones (62), (63) and (69). Similar oxygenation of 13-methoxy- totara-6,8,11,13-triene (21) gives a hydroperoxide (74) which undergoes a facile rearrangement to a naphthyl derivative (80) in the presence of acid. Photo-sensitized oxidation of the enol acetates derived from the 7-oxo diterpenoids, however, provides a general method for preparation of the corresponding 5-ene-7-one. Reduction of the enone (62) with lithium aluminium hydridealuminium chloride gives a mixture of the 5,8,11,13-tetraene (66) and the 6,8,11,13-tetraene (9) while reduction with sodium borohydride and treatment of the resulting alcohols (61) and (67) with acid gives a mixture of the tetraenes (5) and (68). Photo-oxygenation of the latter mixture provides a convenient method for isolating the tetraene (68). Similar reductions of 13-methoxytotara-5,8,11,13-tetraen-7-one (76) have been examined and products from the action of m-chloroperbenzoic acid on the enol acetates (19), (20) and (7) are reported.

Photooxidative dehydrogenation of Δ8-drimen-and Δ8-11-homodrimen-7-ones into α,α ′-dienones

“…The extract was washed with water, a saturated solution of NaHCO 3 , and water, dried with anhydrous Na 2 SO 4 , filtered, and concentrated in vacuo. The liquid residue was chromatographed on a column with SiO 2 (11 g 13 C NMR, δ: 12.63 (C(13)); 15.07 (C(16)); 18.81 (C(2)); 20.72 (C(14)); 22.80 (CH 3 COO); 32.33 (C(15)); 32.87 (C(1)); 33.09(C(4)); 34.84 C(3)); 39.53 (C(10)); 40.69 (C(11)); 51.23 (C(5)); 51.95 (COOCH 3 ); 113.98 (C(6)); 126.12 (C(7)); 139.94 (C(8)); 147.20 (C(9)); 169.65 (CH 3 COO); 172.36 (C(12)). Found: M 320.1984.…”

“…Elution with light petroleum-Et 2 O (3 : 1) gave 48 mg (yield 59%) of diacetoxy diene 9. 13 C NMR, δ: 11.92 (C(12)); 15.73 (C(15)); 18.44 (C(2)); 20.37, 20.82 (both CH 3 COO); 22.53 (C(14)); 32.11 (C(1)); 32.78 (C(4)); 34.43 (C(13)); 38.62 (C(3)); 40.47 (C(10)); 51.19 (C(5)); 59.68 (C(11)); 115.85 (C(6)); 129.00 (C(7)); 139.69 (C(8)); 146.76 (C(9)); 169.30, 170.73 (both CH 3 COO).…”

“…The residue (26 mg) was chromatographed on a column with SiO 2 (2 g). Elution with light petroleum-Et 2 O (4 : 1) gave 10 mg (36%) of 11 acetoxydrimа 5,8 dien 7 one (11) 13 C NMR, δ: 11.02 (C(12)); 18.00 (C(2)); 20.69 (CH 3 COO); 25.13 (C(15)); 28.33 (C(13)); 32.32 (C(14)); 34.32 (C(1)); 37.35 (C(4)); 40.28 (C(3)); 43.29 (C(10)); 60.16 (C(11)); 123.78 (C(6)); 135.20 (C(8)); 154.70 (C(9)); 170.74, (CH 3 COO); 172.62 (C(5)); 186.93 (C (7)). …”

“…Transformation of 11,12 diacetoxydrim 8 en 7 one (12) into enol acetate (13). p Toluenesulfonic acid (4 mg) was added to a solution of oxo diacetate 12 7 (0.18 g, 0.535 mmol) in isopropenyl acetate (2 mL), and the mixture was refluxed under argon until the reaction was over (6 h, TLC monitoring).…”