Positional Isomerization of 1,2-Azaborine through BN-Benzvalene.

Area of Science:

• Organic Chemistry
• Photochemistry
• Heterocyclic Chemistry

Background:

• 1,2-Azaborines are versatile heterocyclic compounds with applications in various chemical fields.
• Synthesizing specific isomers of 1,2-azaborines, particularly C4-aryl derivatives, can be challenging.
• Existing methods often lack generality or regioselectivity for complex substitutions.

Purpose of the Study:

• To develop a novel photochemical strategy for isomerizing C5-aryl-1,2-azaborines to C4-aryl-1,2-azaborines.
• To elucidate the reaction mechanism, including the role of the BN-benzvalene intermediate and the oxidative pathway.
• To demonstrate the broad applicability of this method for synthesizing difunctionalized and hexa-substituted 1,2-azaborines.

Main Methods:

• Photochemical isomerization of C5-aryl-1,2-azaborines.
• Generation and characterization of BN-benzvalene intermediates.
• Deuterium labeling studies to probe reaction pathways.
• Transient absorption (TA) spectroscopy to study reaction dynamics.
• Density Functional Theory (DFT) calculations to support mechanistic understanding.

Main Results:

• A novel photochemical positional isomerization of C5-aryl-1,2-azaborines to C4-aryl counterparts was achieved.
• The reaction proceeds via a BN-benzvalene intermediate and an oxidative radical cation pathway.
• Deuterium labeling, TA spectroscopy, and DFT calculations confirmed the proposed mechanism.
• The method provides the first general route to C4,C5-difunctionalized 1,2-azaborines.
• Regioselective synthesis of hexa-substituted 1,2-azaborine derivatives was accomplished.

Conclusions:

• The developed photochemical approach offers an efficient and versatile route to C4-aryl-1,2-azaborines.
• This method overcomes limitations of previous synthetic strategies for substituted azaborines.
• The findings open new avenues for the synthesis of complex heterocyclic structures with potential applications.