Absolute asymmetric photochemistry using centrosymmetric single crystals. The host/guest system (E)-cinnamamide/E-cinnamic acid

Direct assignment of the absolute configuration of molecules from crystal morphology

“…The four C-atoms of the C4 ring formed by insertion of the acid at the 1b pole of the crystal are of R-absolute configuration, whereas that formed at -b side are of S- configuration. 42 The predicted configuration was confirmed by an independent Bijvoet analysis.…”

“…This reduced symmetry was proven photochemically. 42 Ultraviolet irradiation of Ecinnamamide yields centrosymmetric photodimers, by virtue of a cyclobutane ring formation involving pairs of close packed >C¼ ¼C< bonds across centers of inversion (Fig. 21).…”

Synthetic Organic Chemistry Based on Small Ring Compounds

“…These include [2ϩ2] cycloaddition reactions via photolytic [25][26][27][28][29][30][31][32] and thermolytic [33][34][35][36][37][38][39][40][41][42] processes, enantioselective alkylation, 43) ring contraction of cyclic acetals, 44) radical cyclization, 45) and chemical 46) and enzymatic 47) resolution of racemates or prochiral precursors. In contrast to these well documented methods described above, there have been few studies on the asymmetric induction of the ring expansion reaction of cyclopropane rings to form cyclobutanes.…”

Aspects of spontaneous separation of enantiomers in two- and three-dimensional crystals

“…This concept was taken advantage of to perform asymmetric synthesis within enantiomorphous mixed crystals of cinnamide/cinnamic acid 28 and cinnamide/␤-thienylacrylamide, 29 via solid-state dimerization 30 between host and guest molecules, yielding chiral cyclobutane products.…”