Boron-Containing Heterocycles: Syntheses, Structures, and Properties of Benzoborauracils and a Benzoborauracil Nucleoside

Article abstract of DOI:10.1021/jo991176q

Benzo-fused boron-containing heterocycles (benzoborauracils), 1-hydroxy-1H-2,4,1-benzodiazaborin-3-one (3a), 1-hydroxy-2-methyl-1H-2,4,1-benzodiazaborin-3-one (3b), and 1-hydroxy-2-phenyl-1H-2,4,1-benzodiazaborin-3-one (3c) were synthesized, and their structures were established on the basis of ¹H, ¹³C, and ¹¹B NMR spectroscopies, mass spectrometry, and microelemental analyses. The structures of compounds 3b and 3c were unambiguously confirmed by X-ray crystallographic analyses. ¹¹B NMR spectral analyses of the methanolic solutions of benzoborauracils 3a-c confirmed the formation of the corresponding bis-methanol adducts 13a-c. The structure of the N-Ph bis-methanol adduct 13c was confirmed by X-ray crystallography. The stabilities of these bis-methanol adducts depend on the substituent at the N2 position of 3a-c. The bis-methanol adducts are readily reconverted to the corresponding benzoborauracils upon removal of methanol. The first stable benzoborauracil nucleoside, 4-[5-O-(tert-butyldimethylsilyl)-2,3-O-disopropylidene-α-D-ribofuranosyl]- 1-hydroxy-2-methyl-1H-2,4,1-benzodiazaborin-3-one (25) was prepared in two steps by treatment of 2-aminophenylboronic acid with 5-O-(tert-butyldimethylsilyl)-2,3-O-diisopropylidene-D-ribofuranose followed by its reaction with methylisocyanate.