Photocatalyzed Perfluoroalkylation of Endoglycals

MORA FLORES, ERWIN; DANIEL SUAREZ; MARIA LAURA UHRIG; AL POSTIGO

JOURNAL OF ORGANIC CHEMISTRY

AMER CHEMICAL SOC

Lugar: Washington; Año: 2023 vol. 88 p. 16803 - 16816

0022-3263

The visible light-induced perfluoroalkyl (RF) radical reactions on peracetylglycalsderived from hexoses and pentoses (galactal, glucal, arabinal, and xylal derivatives) wasinvestigated. Various photocatalysts and perfluoroalkyl iodides (RF-I) were employed assources of RF radicals, with LEDs as the irradiation source. Particularly noteworthy wasthe use of an Iridium photocatalyst, Ir[dF(CF3)ppy]2(dtbpy))PF6, which yielded twodistinct product types when applied to glucal. On the one hand, the 2-RF-substitutedglucal, a trend observed even when utilizing organic dyes as photocatalysts. On the otherhand, the unexpected addition product, namely the 1-RF-2-iodo-α-manno-configured Cglycosylderivative was also obtained, as a result of a highly regioselective additionreaction of the RF moiety into the anomeric carbon, followed by attachment of the iodineatom on C-2 in axial disposition. This result contrasted with other radical reactions carriedout onto 2-unsubstituted glycals, where the incipient radical adds to C-2, generating astabilized 1-glycosyl radical. The photocatalyzed radical perfluoroalkylations ofperacetyl glycals derived from galactose, arabinose and xylose all afforded the 2-RFsubstitutedglycals in good yields as a result of the expected vinylic substitution reaction.Mechanistic studies revealed that the 1-RF-2-iodo-α-manno-configured C-glycosylderivatives arise from a radical chain reaction, whereas the 2-RF-substituted glycalsproceed from inefficient chain processes