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<p>One
of the most efficient ways to synthesize oxetanes is the light-enabled [2+2]
cycloaddition reaction of carbonyls and alkenes, referred to as the
Paternò-Büchi reaction. The reaction conditions for this transformation
typically require the use of high energy UV light to excite the carbonyl,
limiting the applications, safety, and scalability. We herein report the
development of a visible light-mediated Paternò-Büchi reaction protocol that
relies on triplet energy transfer from an iridium-based photocatalyst to the
carbonyl substrates. This mode of activation is demonstrated for a variety of aryl
glyoxylates and negates the need for both, visible light-absorbing carbonyl
starting materials or UV light to enable access to a variety of functionalized
oxetanes in up to 99% yield.</p>
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