SOME SUBSTITUTED 9-PHENYLXANTHEN-9-YL PROTECTING GROUPS

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.