A stereoselective, scalable, and metal-free ringexpansion of monocyclopropanated pyrroles and furans has been developed, leading to value-added highly functionalized tetrahydropyridine and dihydro-2H-pyran derivatives. Featuring a cyclopropylcarbinyl cation rearrangement as the key step, the selective cleavage of the unactivated endocyclic cyclopropane C−C bond is achieved. Targeted transformations of the thus obtained sixmembered heterocycles give access to versatile building blocks with relevance for drug synthesis.

Biomass-derived 5-chloromethylfurfural (CMF) can efficiently be functionalised by way of metal-free, Et3B/O2-induced atom transfer radical addition (ATRA) reactions with styrenes.