# On the Mechanism of Random Handedness Generation in the Reactions of Heterocyclic Aldehydes with Diallylboronates

## TL;DR

This study explains how reactions of heterocyclic aldehydes with diallylboronates can produce products with random handedness due to competition between monomers and dimers.

## Contribution

The paper reveals a novel mechanism involving monomeric and dimeric autoinductors causing random enantiomer formation.

## Key findings

- NMR data show that racemic alcohol 3a dimerizes to form mostly the heterochiral dimeric boronate 5a(RS).
- DFT computations confirm strongly exergonic dimerization with ΔΔG298 −6.5 kcal/mol.
- The system's equilibria between monomers and dimers explain the random handedness of the product.

## Abstract

The mechanism of generation of products with opposite handedness in the reactions of heterocyclic aldehydes with diallylboronates was studied by NMR experiments and DFT computations. The origin of this unusual phenomenon is a competition between monomeric and dimeric autoinductors that promote the formation of opposite enantiomers. Thus, NMR data suggest that racemic alcohol 3a, upon dimerization, provides almost exclusively the heterochiral dimeric boronate 5a(RS). This corresponds to the computed results predicting strongly exergonic dimerization with ΔΔG298 −6.5 kcal/mol. Dimerization of the chiral boronate 3a (R) with 82% ee yields 5a (RS) in which all available 3a(S) is bound. As a result, 3 species remain in the solution: (1) 5a(RS), producing a newly formed racemic product in the reaction with 1a, (2) 3a(R), reacting with 1a and yielding an R-configured newly formed product, and (3) 5a(RR), yielding selectively S-configured newly formed product according to computations. Taking into account the equilibria existing between monomers and dimers, the system is capable of demonstrating the experimentally observed random handedness of the newly formed product.