As might be expected, gem-difluorination results in slight increase of electron-acceptor properties relatively to the parent oxetan-2-yl and oxetan-3-yl substituents (14b/14d, σ = 0.17). When the 3,3-diFox is compared to the donor (cyclo)alkyl groups such as cyclobutyl (14e, σ = -0.12), a considerable increase of electronwithdrawing properties is observed. Therefore, it is the oxygen atom which is mainly responsible for the electron-acceptor properties of the 3,3-diFOx functional group. Stability of the 3,3-difluorooxetane moiety. Full profiling of a novel drug candidate necessarily requires metabolic stability assaying as one of the key parameters. At the same time, the chemical stability of the studied molecule often stays out of attention. Considering the known oxetane reactivity, as well as our unsuccessful experience with N-Boc cleavage from compound 10, one could question the 3,3-diFox moiety stability.