CHEMOSELECTIVE AND STEREOSELECTIVE COBALT-MEDIATED [2+2+2]CYCLOADDITION OF ALKYNES WITH URACIL DERIVATIVES - A NOVEL SYNTHETIC ENTRY TO MODIFIED NUCLEOSIDES

The incorporation of the 5,6 double bond of uracil derivatives in the [2+2+2] cyclization with triple bonds-whether those of alkyne substituents on a heterocycle or those of free alkynes-was accomplished by the proven CpCo route, even though the analogous reaction with other heterocycles had failed earlier. Reaction of 1 with 2 to give 3 reveals interesting possibilities, especially with respect to the synthesis of new active substances (R1 = H, CH3; R2 = CH3; sugar moiety, n = 1-3).