CRYSTAL STRUCTURE-REACTIVITY CORRELATIONS IN THE SOLID-STATE PHOTOCHEMISTRY OF N-(TERT-BUTYL)SUCCINIMIDE

In order to provide experimental evidence on the stereoelectronic requ irements for intramolecular hydrogen atom abstraction by carbonyl oxyg en, N-(tert-butyl)succinimide, 1, was investigated by the crystal stru cture - reactivity correlation method. In this method, the success or failure of a given reaction in the crystalline state is correlated wit h the geometric parameters associated with the process as determined b y X-ray crystallography. In the case of N-(tert-butyl)succinimide, the crystal and molecular structure shows that the molecule adopts a conf ormation in which there are very close contacts (d = 2.17-2.24 Angstro m) between the carbonyl oxygen atoms and certain gamma-hydrogen atoms on the tert-butyl group. In accord with these close contacts, ultravio let irradiation of N-(tert-butyl)succinimide in the crystalline state leads to transfer of one of the gamma-hydrogen atoms from carbon to ox ygen. This produces a 1,4-biradical which closes to form a cyclobutano l, and the cyclobutanol undergoes ring opening to afford the final sta ble product, tetrahydro-1H-azepine-2,5-dione, 2. The crystal and molec ular structure of photoproduct 2 is also reported. In contrast to many solid state transformations, there was no discernable melting of the crystals during reaction, and complete conversions of 1 into 2 could b e achieved. The isolated chemical yield of photoproduct 2 from the sol id state reaction (79%) is in fact considerably higher than that repor ted by Kanaoka and Hatanaka for the corresponding solution phase proce ss (49%). This permitted the solid state reaction to be followed to 10 0% conversion by X-ray powder diffractometry, which showed that the pr ocess is a single crystal-to-polycrystalline transformation involving a regular and progressive conversion of 1 into 2 with no obvious diffr action peaks that might be attributable to the intermediate cyclobutan ol.