Synthesis of optically pure 3-(1n.pi.*)-(1S,6R)-bicyclo[4.4.0]decane-3,8-dione, a molecule which is chiral in the excited state only

Low-temp. photooxygenation of (1S,6R)-3-((E,Z)-methoxymethylene)bicyclo[4.4.0]decan-8-one, prepd. in 10 steps from 2,6-dimethoxynaphthalene, yields a mixt. of four isomeric 1,2-dioxetanes I with ee > 98%. Upon thermal decompn., these 1,2-dioxetanes are all precursors for 3-(1np*)-(1S,6R)-bicyclo[4.4.0]decane-3,8-dione (1*), an optically active diketone in its locally excited 1np* state. The optical activity of this mol. is evidenced by the nonvanishing circular polarization in the chemiluminescence of I. The degree of polarization (ge) at 420 nm equals -(1.5 +- 0.3) * 10-3, a value which is similar to that of the regular fluorescence of optically active (1S,6R,8S)-8-hydroxybicyclo[4.4.0]decan-3-one. This similarity implies the absence of substantial racemization in the excited state, whence one concludes that the rate const. for intramol. 1np* energy transfer in 1* is ?109 s-1. The chiroptical results show that localization of excitation energy at the carbonyl at the 3-position of 1* can be achieved by the synthetic route applied, yielding enantiomerically pure 1*, an optically active mol. whose chirality is due solely to the presence of localized electronic excitation energy. [on SciFinder (R)]