The viability of nitrone-alkene (3 + 2) cycloadditions in alkaloid biosynthesis.

Although evidence has mounted in recent years for the biosynthetic relevance of [4 + 2] cycloaddition reactions, other cycloadditions have received much less attention. Herein we used density functional theory (DFT) calculations to assess the viability of nitrone-alkene (3 + 2) cycloaddition reactions proposed to occur during the biosynthesis of several alkaloid natural products (flueggines and virosaines). The results of our calculations indicate that these reactions have low enough intrinsic barriers and diastereoselectivity that they can proceed without enzymatic intervention.