Overriding Norrish Type II to Access Cyclopropanols

Area of Science:

• Organic Chemistry
• Photochemistry
• Synthetic Methodology

Background:

• The Norrish-Yang photocyclization is a key method for synthesizing cyclobutanols.
• Accessing smaller ring systems like cyclopropanols via photocyclization is challenging due to kinetic preferences.
• 1,5-hydrogen atom transfer (HAT) typically dominates over 1,4-HAT in photoexcited aryl ketones.

Purpose of the Study:

• To develop a novel photocyclization strategy for synthesizing cyclopropanols.
• To overcome the kinetic preference for 1,5-HAT in favor of 1,4-transfer.
• To establish a mild and versatile method for accessing valuable cyclopropanol scaffolds.

Main Methods:

• Utilized β-boryl aryl ketones as substrates.
• Employed solvent-controlled selective population of triplet states (π,π* over n,π*).
• Investigated the mechanism of 1,4-boryl group transfer versus 1,5-HAT.

Main Results:

• Demonstrated the first successful photocyclization of β-boryl aryl ketones to cyclopropanols.
• Achieved selective 1,4-boryl group transfer, bypassing the favored 1,5-HAT.
• The reaction proceeds under mild conditions with broad functional group tolerance.

Conclusions:

• This work presents a novel and efficient route to cyclopropanols via photocyclization.
• The developed method provides access to medicinally relevant 3-membered rings previously difficult to synthesize.
• The strategy offers a versatile platform for generating diverse cyclopropanol derivatives.