Protic additives or impurities promote imine reduction with pinacolborane

Area of Science:

• Organic Chemistry
• Catalysis
• Reaction Mechanisms

Background:

• Catalyzed imine hydroboration is a key method for amine synthesis.
• Understanding factors influencing reaction efficiency and selectivity is critical.
• Side reactions can complicate catalytic processes and reduce yields.

Purpose of the Study:

• To investigate the effect of stoichiometric alcohols or water on imine reduction with pinacolborane.
• To explore the role of protic impurities in catalyzed imine hydroborations.
• To identify potential sources of background reactions in imine reduction.

Main Methods:

• Reaction of various imines with pinacolborane in the presence of alcohols or water.
• Screening of chiral additives, including binol, for enantioinduction.
• Analysis of reaction products to determine conversion and selectivity.

Main Results:

• Stoichiometric alcohols or water promote imine reduction with pinacolborane.
• Alkyl imines were reduced, whereas aniline-derived imines showed poor reduction.
• Binol provided modest enantioinduction; other chiral additives were ineffective.
• The presence of protic impurities can lead to significant side reactions in catalyzed imine hydroborations.
• Amines can also promote imine reduction, suggesting potential autocatalysis.

Conclusions:

• Protic impurities, such as water and alcohols, act as promoters for imine reduction with pinacolborane.
• These findings highlight the importance of considering protic impurities as a source of background reactions in catalyzed imine hydroborations.
• The study identifies a potential pathway for unexpected imine reduction and emphasizes the need for careful control of reaction conditions.