ABSTRACT
A single-crystal-to-single-crystal solid-state reaction of vinylogous donor-acceptor cyclopropanes is documented. The enantiospecific synthesis of new products, distinct from those obtained in solution, is achieved for the target compounds. Photopolymerization occurred upon X-ray exposure to the crystals. Notably, in one case, this reactivity exhibits selectivity since an ordered arrangement of polymers and unreacted cocrystallized monomeric conformers has been observed. Structural characterization of the complete transformation monitored through single-crystal X-ray diffraction and supported by molecular dynamics simulations sheds light on the subtle role of crystal packing in the reaction process. Moreover, the X-ray diffraction (XRD)-resolved structure of a donor-acceptor cyclopropane intermediate reveals an elongation in bond length that corroborates the existence of the so-called "push-pull effect".
ABSTRACT
The release of the inherent ring strain of cyclobutane and cyclopropane derivatives allows a rapid build-up of molecular complexity. This review highlights the state-of-the-art of the ring expansions of three- and four-membered cycles and is organised by types of reactions with emphasis on the reaction mechanisms. Selected examples are discussed to illustrate the synthetic potential of this elegant synthetic tool.
