Some substituted 9-phenylxanthen-9-yl protecting groups

Abstract

Xanthen-9-one 8 was converted into 9-(4-methoxyphenyl)-, 9-(4-methylphenyl)- and 9-[3(trifluoromethyl)phenyl]-xanthen-9-ol (10; R¹= OMe, R²= H, 10; R¹= Me, R²= H, and 10; R¹= H, R²= CF₃, respectively). The corresponding 5′-protected thymidine derivatives (13; R¹= OMe, R²= H, 13; R¹= Me, R²= H and 13; R¹= H, R²= CF₃) were obtained in satisfactory yields from thymidine 12 and the appropriate 9-chloro compounds (11; R¹= OMe, R²= H, 11; R¹= Me, R²= H and 11; R¹= H, R²= CF₃). In the same way, 2,7-dibromoxanthen-9-one 14 was converted into two 9-aryl-2,7-dibromoxanthen-9-ols (compounds 15a and 15b). Reaction between thymidine 12 and the corresponding 9-chlorocompounds gave the 5′-protected thymidine derivatives 16a and 16b, also in satisfactory yields. The rates of acid-catalysed cleavage of the above five 5′-protected thymidine derivatives (13; R¹= OMe, R²= H, 13; R¹= Me, R²= H and 13; R¹= H, R²= CF₃), 16a and 16b were compared with those of 5′-O-(9-phenylxanthen-9-yl)thymidine 13; R¹= R²= H and 5′-O-(triphenylmethyl)thymidine 3a; B = thymin-1-yl under the same conditions.