Über Dienketene aus o‐Chinolacetaten

Abstract

(RS)- 6-acetoxl.-5,.6-dimeth?.l-, (RS)-6-ucetoxy-2,4,6-1rimeth~.l-, 3,4,6-tet r m n i 4 i j~l -. and (RS)- 6-oci~tox~-2,3,4,5,6-pentumeth~l-2,4-c~clo/ie.~udii~n-I-oni~.~ serve as representative educts.Thcrc arc two separate main photochemical routes conveniently designated as l(n*, n) or '(n*, n ) tracks. The latter may also he attained by sensitization and leads to phenols. The former, by a-cleavage furnishes dien-ketens as indispensable phototransients. Photolysis of dien-ketens follows one or more of three reaction channels, each of which yields a particular type of photoproduct: heat-induced monocyclization affords 2,4-cyclohexadien-1-ones, heat-induced hicyclization stereoselectively furnishes bicyclo[3.1.0]hex-3-en-2-ones, and multi-step addition of protic nucleophiles stereosclcctively gives l,4-, I,6-and/or 1,2-adducts. By X-ray analysis or NOE studies, the structure of isolated photoproducts is establishcd. Conventional spectroscopy at low or flash spectroscopy at normal temperature yield information on the Cormation and decay of kinetically unstable intermediates. Photoproduct composition depends on the pattern o C substitution of the educts, o n thc solvents, and on the nucleophiles that might he present. Substituents primarily exert an influence upon the population of the various conformers of the dien-ketcn. Solvents affect the rate of the divers reaction paths competing for the phototransient. Nucleophiles play more than a trivial role when adducts are formed. With the detailed view of a dien-keten's role on hand, the photoproduct from a given o-quinol-acetate -or more general from a linear conjugatcd cyclohexadienone -is now predictable.

Substituent and solvent influence on the nature of the oxyallyl intermediate in the rearrangement of bicyclo[3.1.0]hex-3-en-2-ones

“…It has been suggested that oxyallyl compounds are intermediates in both thermal and photochemical rearrangements of bicyclo[3.1.0]hex-3-en-2-ones to phenols [25][26][27][28][29][30][31][32][33][34][35]. Some time ago, we studied the reaction pathway for the prototype rearrangement of bicyclo[3.1.0] hex-3-en-2-one (1a) to phenol (3a) in the gas phase at the CASSCF/CASPT2 level [36].…”

Calculated pKEnol Values for Enols of Carboxylic Acid Derivatives HCC(OH)X (X = OH, NH2, NMe2, OMe, OCHO, F, Cl, Br)

“…Enols of acids were suggested as intermediates in the decarboxylation of a dicarboxylic acid,3a in the reductive debromination of a carboxylic acid,3b in the nitrosation of malonic acids,3c and in the Hell−Volhard−Zelinskii bromination of acids 3d. Enols of esters, acyl halides, and amides were suggested as intermediates in nitrosation of XCH 2 CO 2 Et (X = H, CN)4a and addition of alcohols 4b or H−Hal 4c to ketenes, water addition to ketenimines,4d and electrophilic substitution of malonamide,4e respectively. A conjugated enol amide was observed by UV in a low-temperature photolysis of a dienone in the presene of an amine 4f…”

Quantum yields in the photochemically induced radical chemistry of acyl derivatives of thiohydroxamic acids

“…548,11 This compound has a well-documented history of photochemistry546 and a known quantum yield ( = 0.53 (365 nm, 20 °C))55 at a specific concentration. 56 We observed only one isomer,57 and we were able to reproduce this quantum yield (0.52).…”