Photochemistry of α-diketones in carbohydrates: anomalous Norrish type II photoelimination and Norrish-Yang photocyclization promoted by the internal carbonyl group.
A series of four α-diketones placed as 1α-pyruvoyl tethers on D-glucopyranose and D-glucopyranosiduronic acid skeletons was prepared in order to determine the influence of captodative and stereoelectronic effects on the regioselectivity of the hydrogen atom transfer (HAT) in Norrish type II photochemical processes. We observed that the 1,5-HAT regioselectivity can be switched between the two potentially abstractable syn-1,3-diaxial hydrogens at H6 and H8. Highly unusual photoproducts from Norrish type II photoelimination and Norrish-Yang photocyclization initiated by the excited internal carbonyl group were obtained, in some cases in excellent synthetic yield. The 1,5-HAT transition state in the Norrish type II photoelimination was investigated by photochemical experiments in the crystalline state.
Instituto de Productos Naturales y Agrobiología del C.S.I.C. Carretera de la Esperanza 3, 38203 La Laguna, Tenerife (Spain), Fax: (+34) 922-260-135.
Dimitri
D
Alvarez-Dorta
Elisa I
EI
León
Alan R
AR
Kennedy
Angeles
A
Martín
Inés
I
Pérez-Martín
Concepción
C
Riesco-Fagundo
Ernesto
E
Suárez
D002241:Carbohydrates / Q000737:chemistry*; D003500:Cyclization; D007659:Ketones / Q000737:chemistry*; D015394:Molecular Structure; D055668:Photochemical Processes; D010777:Photochemistry; D011773:Pyruvates / Q000737:chemistry*
D002241:Carbohydrates; D007659:Ketones; D011773:Pyruvates
carbohydrates; cyclization; diketones; photochemistry; radicals