Photochemical synthesis of benzoyl spiro[2.2]pentanes.
In the present study, we describe the photochemical behaviour of 2-mesyloxy phenyl ketones 8 and 12 bearing a cyclopropane moiety in the side-chain. Irradiation of 8 and 12 leads to the corresponding benzoyl spiro[2.2]pentanes as a consequence of an initial gamma-H-shift, subsequent elimination of MsOH (accompanied by a spin-center shift) and cyclization of the resulting 1,3-diradicals. In contrast, a corresponding phenyl ketone without a mesyloxy group in the 2-position, and thus a potential reactant of the "classical" Norrish-Yang reaction, shows no photochemical reaction. By means of quantum chemical calculations we discovered that in the presence of a mesyloxy group the activation barrier for the photochemical gamma-H-shift is substantially decreased. Furthermore, a photoinduced skeletal rearrangement of benzoyl spiro[2.2]pentane to 2-cyclobutylidene-acetophenone could be observed. Compared to the common methods used to synthesize spiro[2.2]pentanes, the photochemical preparation of benzoyl spiro[2.2]pentane presented herein is the first example where a bond between the spiro atom and an adjacent atom is formed.
Muehling
Olaf
O
Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Str., 2, 12489, Berlin, Germany.
Wessig
Pablo
P
D003500:Cyclization; D015394:Molecular Structure; D010420:Pentanes / Q000138:chemical synthesis*; D010777:Photochemistry; D011789:Quantum Theory; D021241:Spectrometry, Mass, Electrospray Ionization
D010420:Pentanes