“Armed and disarmed” theory in the addition of an azide radical to glucals

In this report, “armed and disarmed” theory was used to explain the selectivity of azide radical addition to glucals. We discovered that “armed” glucals were prone to undergo a kinetic process. The torsional strains govern the selectivity. Meanwhile, “disarmed” glucals preferred thermodynamic radical addition. We also applied our method to synthesize a sialic acid containing trisaccharide.