The first boron-containing 2',3'-cyclic phosphate-modified analogue, uridine 2',3'-cyclic boranophosphate (2',3'-cyclic-UMPB), was synthesized. 5'-O-Protected uridine was cyclophosphorylated by diphenyl H-phosphonate to yield uridine 2',3'-cyclic H-phosphonate, which upon silylation followed by boronation and subsequent acid treatment gave 2',3'-cyclic-UMPB in high yield. The two diastereomers of 2',3'-cyclic-UMPB were separated by HPLC. An alternative method for synthesis of uridine 2',3'-cyclic phosphorothioate (2',3'-cyclic-UMPS) via H-phosphonate was also described.