Gunnar Olovsson

CONTROL OF THE SOLID-STATE PHOTODIMERIZATION OF SOME DERIVATIVES AND ANALOGS OF TRANS-CINNAMIC ACID BY ETHYLENEDIAMINE

Some of double salts derived from ethylenediamine (en) and a variety of trans-cinnamic acids and their analogs underwent photodimerization in the solid state, giving predominantly β-truxinic dimers. X-Ray studies demonstrate that (a) the conformation of en is gauche for the highly photoreactive double salts (o-1b·en and m-1e·en), whereas it is anti for lessphotoreactive o-1a·en or photoinert 1d·en and (b) for highly reactive o-1b·en and m-1e·en, the monomer acid molecules are arranged in an overlap configuration and a reactive monomer pair is hydrogendashbonded to the same en molecule.

ABSOLUTE CONFIGURATION CORRELATION STUDIES IN SOLID STATE ORGANIC PHOTOCHEMISTRY

An ever-increasing number of examples in the literatun? attest to the fact that photochemical reactions carried out in optically active crystalline media can lead to enantioineridly enriched products in high optical yields. Taken from our own work and that of others, this article examines the relatively few examples of such reactions in which the absolute stereochemical arrangements of the molecules in the reactant crystals are correlated with the absolute configurations of the optically active products formed by irradiation of the same crystals. Studies of this type provide penetrating insights into the mechanisms of the reactions in question, and in addition, help to pinpoint the crystal latticederived stereoelectronic factors that arc responsible for tbe observed enantioselectivities.

Crystal engineering for absolute asymmetric synthesis through the use of meta-substttuted aryl groups

Abstract A significant tendency towards crystallization in chiral space groups has been found for 4-benzyloxy-2-pyridones whose phenyl groups are meta -substituted ( m -Cl, m -Br, m -Me and m -OMe). Irradiation of single crystals of three of these materials leads to optically active β-lactam derivatives in high chemical and optical yields via an allowed disrotatory electrocyclization.

The novel photochemical behavior of triptycene-1,4-quinone

Abstract Triptycene-1,4-quinone ( 1 ) reacts photochemically in solution to give different products depending on the solvent employed and on the presence or absence of oxygen. The structures of the photoproducts have been elucidated by spectroscopic methods, independent synthesis and single crystal X-ray diffractometry, and possible mechanistic pathways leading to their formation are presented and discussed. Unexpectedly, quinone 1 was found to be photochemically inert in the crystalline state. The X-ray crystal structure of 1 reveals the probable reason for this behavior.

NOVEL DIFFERENCES BETWEEN THE SOLID STATE AND SOLUTION PHASE PHOTOCHEMISTRY OF 1,2-CYCLODECANEDIONE

Abstract 1,2-Cyclodecanedione ( 1 ) undergoes a novel photorearrangement in the crystalline state that is different from the Norrish/Yang type II photocyclization process observed in solution. A possible mechanism is presented and discussed.

Cation to anion triplet-triplet energy transfer in crystalline organic salts

Irradiation of crystalline salts formed between sensitizer-linked amines and photochemically reactive carboxylic acids at wavelengths where only the sensitizers absorb leads to characteristic triplet state reactivity of the carboxylate anions.

Modification of host photobehavior by formation of crystalline host-guest assemblies

Abstract 9,10-Dihydro-9,10-ethenoanthracene-11,12-bis(diphenylmethanol) ( 1 ) forms stable crystalline complexes with ethanol, acetone and toluene. In solution, diol 1 undergoes the di-π-methane photorearrangement, but irradiation of the complexes in the crystalline state leads to a novel dehydration reaction. X-ray crystallography reveals the probable source of this difference in behavior: pre-organization of the hydroxyl groups in the solid state in a hydrogen-bonded arrangement that is particularly favorable for dehydration.

Unusual photorearrangements of 9,10-disubstituted triptycene-1,4-quinone derivatives

Abstract In contrast to triptycene-1,4-quinone ( 1a ), which forms exclusively a di-π-methane type product when irradiated in acetonitrile, photolysis of the 9,10-dialkyl-substituted triptycene quinones 1b and 1c leads to carbene-derived as well as hydrogen atom abstraction-derived photoproducts. Mechanistic schemes that are capable of rationalizing the results on stereoelectronic grounds are presented and discussed.

Structures and Photochemistry of Inclusion Compounds of 9,10-Dihydro-9,10-ethenoanthracene-11,12-bis(diphenylphosphine Oxide)

Inclusion complexes of 9,10-dihydro-9,10-etheno-anthracene-11,12-bis(diphenylphosphine oxide) (1) as host are synthesized using a variety of guest solvent molecules and the photochemistry of the host molecule is studied in solution and in the crystalline complexes. The crystal structures of four complexes are determined and correlated with their photochemical reactivity. In each case only one dibenzosemibullvalene photoproduct is obtained in the photolysis. Since three of the complexes studied crystallize in the chiral space group P212121, irradiation of single crystals produces a chiral photoproduct in >90% enantiomeric excess. Determination of the absolute configurations of reactants and products allows elucidation of the key structural features that control the enantiospecific solid-state photorearrangements.

Photochemistry of Triptycene-1,4-quinone

Photolysis of 9,10-dihydro-9,10[1′,2′]benzenoanthracene-1′,4′-quinone, C20H12O2, in oxygenated acetone gives the novel photoproduct 9,10-dihydro-9,10-ethanoanthracene-11-one-12-spiro-2′-cyclopent-4′-ene-1′,3′- dione, C20H12O3. The reactant quinone molecule has ideal mm symmetry and lies on a crystallographic mirror plane in Pnma; the photoproduct molecule has ideal m symmetry, which is not utilized in packing in Pna21. This product is formed only in the presence of oxygen and a mechanism for its formation is proposed. Unreactivity in attempted solid-state photolysis can be rationalized in terms of crystal packing.