Photogenerated Oxetanes as a Gateway to Uphill Cyclopropanation

ABSTRACT Despite their privileged status in pharmaceutical chemistry, the sustainable synthesis of cyclopropanes remains a fundamental challenge. Conventional methods rely on hazardous diazo precursors or pre‐functionalized substrates that generate stoichiometric byproducts. Here, we report an overall endergonic, catalytic route to cyclopropanes from abundant, renewable starting materials. Furan oxetanes, readily formed by photochemical [2 + 2] cycloaddition of aldehydes and furan, undergo an intramolecular S N ‐type rearrangement under Lewis acid catalysis, producing cyclopropanes with ideal atom economy. The strategy enables access to meso ‐cyclopropane dicarbaldehydes, which are versatile intermediates that streamline the preparation of otherwise challenging bioactive motifs. By harnessing photogenerated oxetanes as cyclopropane precursors, this work offers a sustainable way to densely functionalized cyclopropanes from simple feedstocks under mild conditions.