T. Y. Fu

Ionic chiral handle-induced asymmetric synthesis in a solid state Norrish type II photoreaction

Abstract Irradiation of crystals of salts formed between 4-(2,4,6-triisopropylbenzoyl)benzoic acid ( 1a ) and various optically active amines is shown to lead to optically active Norrish type II photoproducts in low to moderate enantiomeric excesses, a process in which the ammonium ion has acted as an “ionic chiral handle.” X-ray crystallography reveals that the salts crystallize with two independent, mirror image-related molecules of the benzophenone moiety in the asymmetric unit, and this is suggested to be the source of the low ee s observed.

Phenyl[2,4,6-tris(1-methylethyl)phenyl]-methanethione and 4-methoxyphenyl[2,4,6-tris(1-methylethyl)phenyl]methanethione

The two title compounds, C 22 H 28 S and C 23 H 30 OS, respectively, have almost identical molecular structures, but different crystal structures. The two parts of each molecule are approximately perpendicular to each other, with S...γH distances of 3.06 and 3.02A, respectively, suitable for H-atom abstraction in photochemical reactions.

4-[2,4,6-Tris(1-methylethyl)benzoyl]benzoic acid (S)-(-)-proline

The title compound, C 23 H 28 O 3 .C 5 H 9 NO 2 , is a 1:1 complex of the benzoic acid derivative and the (S)-proline zwitterion, with two formula units in the asymmetric unit (with pseudo-symmetry relationships between the separate components). The ketone carbonyl group in each benzoic acid molecule deviates slightly from a position normal to the plane of the triisopropylphenyl ring; the deviations (of about 16°) are in opposite senses in the two molecules, so that the molecules have opposite conformational chiralities, leading to a nearly racemic photoproduct on solid-state photolysis.

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.

[(1,2,5,6-η)-1,5-Cyclooctadiene][(11R,12R)-9,10-dihydro-9,10-ethanoanthracene-11,12-bis(diphenylphosphino-P)]rhodium(I) Tetrafluoroborate

The title compound, [Rh(C 8 H 12 )(C 40 H 32 P 2 )]BF 4 , which functions as an asymmetric catalyst, contains a five-membered chelate ring, and has molecular geometry and dimensions similar to those in related materials.

3-(4-Cyanophenyl)-2,2-dimethyl-1-phenylpropane-1-thione

The title molecule, C18H17NS, contains an all-trans arrangement of the central aliphatic system and exhibits an intramolecular S⋯βH contact of 2.71 A, which is favourable for hydrogen abstraction in a photochemical reaction. The angular parameters (describing the orientation of the H atom relative to the thiocarbonyl plane) are close to those expected for reaction via the (n,π*) excited state.

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.

(Z)-1-Benzoyl-4-tert-butyl-1-methylcyclohexane and (Z)-4-tert-Butyl-1-methyl-1-thiobenzoylcyclohexane

Both title molecules, C 18 H 26 O and C 18 H 26 S, contain six-membered cyclohexane rings with chair conformations, equatorial 1-methyl and 4-tert-butyl substituents, and axial 1-benzoyl or 1-thiobenzoyl substituents, respectively. The substituent carbonyl and thiocarbonyl groups are oriented with the O and S atoms close to axial H atoms in the cyclohexane rings, thus accounting for the observed photochemical reactivity.

N-phenyl-N-(phenylthioxomethyl)benzamide

The title molecule, C20H15NOS, adopts an (ES,ZO) conformation, similar to that of other monothioimides, with an intramolecular O⋯C(S) contact of 2.821 (5) A; a photochemical cleavage reaction probably proceeds via intramolecular nucleophilic attack of oxygen on the C=S double bond in the presence of solvolytic agents.

Structure and Photochemistry of Four Adamantylacetophenones

The photochemistry and crystal structures of four α-adamantylacetophenones have been studied, namely, 1-(4-fluorophenyl)-2-(tricyclo[3.3.1.13,7]dec-1-yl)ethanone [(1a), C18H21FO], 1-(4-cyanophenyl)-2-(tricyclo[3.3.1.13,7]dec-1-yl)ethanone [(1b), C19H21NO], 1-(4-cyanophenyl)-2-(3-methyltricyclo[3.3.1.13,7]dec-1-yl)ethanone [(1c), C20H23NO] and 1-(4-carboxyphenyl)-2-(3-methyltricyclo[3.3.1.13,7]dec-1-yl)ethanone [(1d), C20H24O3]. All four molecules adopt fairly similar conformations, with short γH⋯O contacts permitting hydrogen abstraction in the photochemical reactions. However, three of the compounds, (1a), (1b) and (1d), are photostable in the solid state and possible reasons for this unreactivity are considered.