Photochemical transformations of small ring heterocyclic compounds. LXII. Competitive keto-enolate photochemistry in the 3-phenylcoumaran-2-one system

Abstract

20) The g factor observed is larger than those of simple alkyl radicals. It is due to the large spin-orbital coupling constant of sulfur atom (£p = 382 cm-1) as compared with that of carbon atom (¿jp = 28 cm-1).

The generation and reactions of quinone methides

“…Xanthene was proposed to form by intramolecular electrocyclic addition reaction of o- 2 followed by a 1,3 hydrogen shift (Scheme 5B). 15 The photochemical decarbonylation of 2,4,5-trimethylhomogenistic lactone gives the 2-hydroxy-1,3,4-trimethyl- o -quinone methide. 16 The o -thioquinone methide has been generated by decarbonylation of benzothiolactone (Scheme 4B, X = S) and trapped by N-ethylmaleimide.…”

UV-induced unimolecular photochemistry of 2(5H)-furanone and 2(5H)-thiophenone isolated in low temperature inert matrices

“…The photochemistry of five-membered heterocyclic a-carbonyl compounds in different solutions was studied by several authors for a long time [2][3][4][5]. Margaretha and co-workers [6][7][8][9][10][11][12][13][14][15][16][17] reported that upon irradiation 2(5H)-thiophenones behave quite differently from the corresponding oxygen-based heterocycles.…”

Construction of the Complete Aromatic Core of Diazonamide A by a Novel Hetero Pinacol Macrocyclization Cascade Reaction

“…[3] Complete reduction of the lactone with LiBH 4 was followed by the smooth formation of dihydrobenzofuran 10 in 95 % yield upon heating the resultant diol with 1,1'-carbonyldiimidazole in THF at reflux, a result which has been previously reported in related systems except under far more forcing conditions. [15] Subsequent conversion of 10 to boronate 11 was then achieved in 70 % yield by using the conditions developed by Ishiyama et al [16] For the purposes of this model study, lactone 9 was also accessed through initial reaction of mandelic acid (12) with 2-bromophenol (13) using Padwa×s method, [17] followed by facile elaboration of 14 to 9, [18] which enabled the synthesis of boronate 11 in just six linear synthetic operations.…”