The efficiency of aromatic ketones as singlet-oxygen ('02('Ag)) sensitizers can vary considerably with the electronic configuration of their lowest triplet state and the solvent used. Near-infrared measurements of the luminescence of singlet oxygen have shown that the quantum yield of singlet-oxygen production (Gd) by 1H-phenalen-I-one (1) is close to unity in both polar ( @, , = 0.97zk0.03 in methanol) and non-polar solvents ( @ A = 0.93+0.04 in benzene). Analysis of the absorption spectra of the ground state and phosphorescence measurements show that the lowest singlet and triplet states have dominant x , A * electronic configurations. The quantum yield of intersystem crossing (cDISc) of 1, determined by laser flash photolysis (partial-saturation method), is equal to unity. In comparison with other aromatic ketones, these parameters are important for the discussion of the surprisingly high GIsc of 1 and the efficient energy transfer from its triplet state to molecular oxygen. The Iff-phenalen-1-one (l), being one of the most efficient singlet-oxygen sensitizers in both polar and non-polar media, could be used as a reference sensitizer, in particular in the area of relatively high energies of excitation.Introduction. -Because of the relatively small energy difference between the ground state (' Z;) and the ('A,) excited state of molecular oxygen (94.2 kJ .mol-'), singlet oxygen ('02('Ag)) should be easily produced by energy transfer from the lowest triplet state of most sensitizers to molecular oxygen (Eqn. I). However, only few sensitizers are of practical use for the generation of singlet oxygen, an activated oxidizing species which plays an important role in photo-oxidation reactions (type-I1 photo-oxidation) [ 1-71.

The axially dissymmetric diphosphines (-)-(R)-and (+)-(S)-(6,6'-dimethylbiphenyl-2,2'-diyl)bis(diphenylphosphine) ((-)-(R)-10 and (+)-(S)-10; 'BIPHEMP') have been synthesized, starting from (R)-and (S)-6,6'-dimethylbiphenyl-2.2'-diamine ((R)-and (S)-16), respectively, via Sundmeyer reaction, lithiation, and phosphinylation. Moreover, racemic 4,4'-dimethyl-and 4,4'-bis(dimethylamino)-substituted analogues 11 and 12, respectively, and the 6,6'-bridged analogue 1,l l-bis(diphenylphosphino)-5,7-dihydrodibenz[c, eloxepin (13) were synthesized and resolved into optically pure (R)-and (S)-enantiomers via complexation with di-p-chlorobis{. The molecular structures of the diphosphines (S)-10 and (R)-13 and of two derived cationic Rh (1) complexes, [Rh((S)-lO)(nbd)]BF, and [Rh((R)-13)(nbd)]BF4were determined by X-ray analyses. Absolute configurations were established for (+)-(S)-10 by X-ray analyses of both the free diphosphine and of the derived Rh(1) complex, and for (-)-(R)-l3 by X-ray analysis of the derived Rh(1) complex. Configurational assignments for the substituted BIPHEMP analogues 11 and 12 were achieved by means of 'H-NMR comparisons of the Pd(I1) complexes derived from the diphosphines and (R)-18, and by means of CD comparisons. The BIPHEMP ligand 10 and analogues 11, 12, and 13 are the first examples of optically active bis(triary1phosphines) containing the axially dissymmetric biphenyl moiety. All these new diphosphines proved to be excellent asymmetry-inducing ligands in Rh(1)-catalyzed isomerizations of N,N-diethylnerylamine affording citronella1 enamine of 98-99% ee.

~~It is shown that dimethyl 7-isopropyl-5, IO-dimethylheptalene-1,2-dicarboxylate (1) and dimethyl 5,6,8,10-tetramethylheptalene-l,2-dicarboxylate (2) can be resolved via the corresponding mono-acids and with the aid of optically active primary or secondary amines such as I-phenylethylamine or ephedrine into the (-)-(P)-and (+)-(M)-enantiomeres, respectively. Characteristic for the (P)-chirality of the heptalene n-skeleton with C, or pseudo-C, symmetry are two (-)-CE's at the long wavelength region (450-300 nm) followed by at least one intense (+)-CE at wavelengths about or below 300 nm. The absolute configuration of the heptalenes was correlated with the well-established absolute configuration of (+)-(R)-and (-)-(S)-l -phenylethanol.

Allocolchicinoids are analogues of the important antimitotic compound (-)-colchicine 1. A strategy is reported for the synthesis of ring C functionalized allocolchicinoids, which is based on a Diels-Alder reaction-aromatization sequence. This route is complementary to the previously disclosed benzannulation approach involving Fischer carbene complexes and alkynes. Dienes 12 and 14 incorporate the natural substitution pattern on ring A and undergo Diels-Alder reactions with various dienophiles. Subsequent aromatization affords the set of differently functionalized ring C allocolchicinoids 15-19, 23, and 25, with high regioselectively and in moderate to good yields. An intramolecular Diels-Alder reaction-aromatization sequence allows for access to allocolchicinoids with reversed regiochemical introduction of ring C substituents. The equilibria of the atropisomers of 15 and 19 are studied in three NMR solvents. Reactions of the dienes 12 and 14 with DMAD lead to the corresponding cycloadducts, but the subsequent aromatization is complicated. A regioselective Diels-Alder reaction-aromatization sequence is utilized as the key step in the first stereoselective total synthesis of (-)-allocolchicine 2. Asymmetric introduction of hydroxy group at C7 is achieved by the enantioselective reduction of ketone 29. The correct stereochemistry is then established by Mitsunobu inversion reaction using Zn(N(3))(2)-2Py.