Synthetic Aspects of the Di-π-methane Rearrangement

Photochemische Reaktionen als Schlüsselschritte in der Naturstoffsynthese

“…[178] Beide Umlagerungen spielen in der Naturstoffsynthese eine weitaus weniger wichtige Rolle als die Oxadi-p-Methanumlagerung. Die Di-p-Methanumlagerung verläuft typischerweise als Singulettprozess, während die Azadi-p-Methanumlagerung sensibilisiert durchgeführt wird.…”

Conformationally Driven Two- and Three-Photon Cascade Processes in the Stereoselective Photorearrangement of Pyrroles

“…An optimization study showed that a ketone in the 2-position of the pyrrole was essential to enable lactam formation (Table 3, entries [1][2][3][4][5] and that a second ketone was actually deleterious to the process (entry 6). Although yields averaged around 50%, this in itself is quite remarkable as intense, high energy 254 nm UV light is used and the successful formation of 22 relies on 3-successive and independent photon mediated events.…”

“…Against this backdrop we wished to explore whether functional groups (R 2 /R 3 ) on the butenyl side chain of pyrrole 4 would influence the outcome of this complex photochemical sequence and lead to single diastereomers of sp 3 -rich aziridines as reactive scaffolds 9 for use in drug discovery. Initially we focused on synthesizing a range of 2-substituted pyrroles (R 1 = CO-Aux) bearing common chiral auxiliaries such as (+)-menthol, Evans' auxiliary, camphor sultam, borneol, and various chiral amines.…”

Synthesis and Chemistry of Polycyclic Aromatic Hydrocarbons with Curved Surfaces: Buckybowls

“…We later learned that light was responsible for the spectral changes and brief (15 min) irradiation of the sample with a sun lamp converted 47 to a new species which was identified as dicorannulenobullvalene 48 [39]. This photochemical barrelene-semibullvalene conversion, known since 1966 [40], represents a sub-class of the di-p-methane rearrangement [41]. However, the conversion of 47 to 48 is, as far as we are aware, the first reported example induced by visible light since all previous conversions were achieved under UV irradiation.…”