Synthesis and computational analysis of densely functionalized triazoles using o-nitrophenylalkynes

Dipolar cylcoadditions with azides using a series of o-nitrophenylethynes and disubstituted alkynes were studied experimentally and computationally. Density functional theory computations reveal the steric and electronic parameters that control the regioselectivity of these cycloadditions. Several new substrates were predicted that would either give enhanced regiocontrol or invert the regiochemical preference. Experimentally, the alkynes were screened in the [3 + 2] cycloaddition with benzyl azide. Of the 11 alkynes screened experimentally, the acetylenes containing halogen substitution directly on the alkyne provided the highest levels of regioselectivity. These haloalkynes were also shown to tolerate variation of the azide moiety with continued good levels of regioselectivity in most cases. Diverse functional groups can be incorporated through the cycloaddition process and their subsequent orthogonal modification was demonstrated.     

Diastereoselective Synthesis of and Mechanistic Understanding for the Formation of 2‐Piperidinones from Imines and Cyano‐Substituted Anhydrides

2‐Piperidinones are synthesized in a single step from imines and 2‐cyano glutaric anhydrides. The reaction provides the products in good diastereoselectivity and generates a quaternary stereogenic center. Substitutions on the anhydride skeleton are well tolerated to provide 2‐piperidinones with three stereogenic centers from a single transformation. The pertinent transition structures have also been computed using quantum mechanics and reveal the key interactions controlling the stereochemical outcome of the reaction.