Tatyana's Research Blog

The Selectivity of Maltol and Allomaltol Oxidopyrylium [5+2] Cycloaddition Reactions

One topic that fascinates Ryan Murelli, Ph.D.'s research group is the oxidopyrylium [5+2] cycloaddition reaction, which is the reaction between an oxidopyrylium ylide and a dipolarophile. This reaction leads to the formation of seven-membered carbocycles and has extensive use in synthesis. The molecules of interest are maltol and its isomer, allomaltol, in their ylide and cycloadduct forms.

A previous lab member studied this cycloaddition reaction using maltol and allomaltol ylides and various dipolarophiles. During his experiments, he observed the formation of 2:1 ylide/alkyne adducts, referred to as “pincer complexes”. These pincer complexes, which emerge from two subsequent [5+2] cycloadditions, formed with surprisingly high regio- and stereoselectivities. Thus, it was worthwhile to gain a more detailed mechanistic insight leading to selective product formation.

The cycloaddition reactions can theoretically lead to up to eight different regio- and stereoisomers, depending on the approach between the dipolarophile and the ylide. We first wanted to explain the selective product formation using computational methods. To do this, the reactions were modeled using the Maestro Schrodinger software with M06-2X/6-311G** as the theory and basis set. According to the results, the selective products that were experimentally observed had the smallest transition state energies, leading us to believe that the product formation is kinetically driven.

My current research is focused on building onto this discovery by exploring new cycloaddition reactions. More specifically, the pincer complexes formed by crossing over the allomaltol ylide with the maltol-derived dipolarophile and the maltol ylide with the allomaltol-derived dipolarophile. The molecules will be characterized using techniques such as nuclear magnetic resonance (NMR) and infrared (IR) spectroscopies. After the characterization, it will be possible to conclude if the favored products of the “cross over” pincer complexes are also kinetically driven. I aim to determine which products are favored and why, and to see if this knowledge can be applied to different cycloaddition reactions.