A cationic cyclometalated iridium complex with a triarylamine donor attached to the primary ligand sphere showed long-lived (0.04 and 1.7 micros) charge-separated states after photoexcitation which are due to a combined Marcus inverted region effect and spin-selection rules.

Oxidation of (3R)-linalool (2) with tert-butyl hydroperoxide (TBHP) occurs at the 6,7-position to selectively afford linalool oxide cis-1, if catalyzed by vanadium(V) Schiff base complexes 4. Substituted tetrahydrofuran cis-1 and its isomer trans-1 served as starting materials for short concise syntheses of β-carbolines cis-3 and trans-3 which are lower homologues of alkaloids (-)-isocyclocapitelline and (+)-cyclocapitelline.(-)-Isocyclocapitelline (Scheme 1), (+)-cyclocapitelline, and (+)-chrysotricine are tetrahydrofuran-derived β-carboline alkaloids, which have been extracted from far eastern medicinal plants. 1,2 From a biosynthetic point of view it seems likely that linalool oxides 1 and therefore linalool 2 serve as precursors for the formation of these alkaloids. 1,3 In organic synthesis, however, the abovementioned β-carbolines are generally obtained in multistep transformations that use other precursors than terpenol 2 as starting material for the following reasons. 4 Conversion of substrate 2 into functionalized tetrahydrofurans 1 requires selective oxygenation at the 6,7-π-bond which is attainable by e.g. peracids 5 or the combination of H 3 CReO 3 /H 2 O 2 . 6 Unfortunately, the observed diastereoselectivities in these reactions are negligible. If oxidized with tert-butyl hydroperoxide in the presence of an early transition metal catalyst such as VO(acac) 2 , 7 a selective conversion of linalool 1 into the corresponding 1,2-epoxyalcohol has been reported. 8,9 In view of the significance of linalool oxides 1 as versatile building blocks, 10 and the contemporary interest in tetrahydrofuran-derived β-carboline alkaloids, 1,2,4 we have developed a new stereoselective access to furanoid linalool oxide cis-1 and disclose our latest results in this communication as a part of the synthesis of hitherto unknown β-carbolines cis-3 and trans-3.The selected strategy for diastereoselectively oxidizing substrate 2 at the 6,7-position is based on the use of TBHP as primary oxidant and vanadium(V) Schiff base complexes 4 as catalysts. 11 The latter reagents were chosen for this purpose, since vanadium compound 4a does not catalyze the epoxidation of allylic alcohols 12 but efficiently mediates diastereoselective formation of functionalized tetrahydrofurans from bishomoallylic alcohols and TBHP. 11,13,14 In an initial experiment, terpenol 2 was treated with TBHP and 10 mol% of vanadium(V) catalyst 4a in CHCl 3 at 20°C for 12 hours. Previous optimization studies had shown that these conditions provide high selectivities for tetrahydrofuran formation in combination with a satisfactory peroxide efficiency. 14 Purification of the reaction mixture furnished furanoid linalool oxides 1 (62%, cis:trans = 61:39), 1,2-epoxylinalool oxides 5 (6%, cis:trans = 56:44), and pyranoid linalool oxides 6 (3%, cis:trans = 40:60) (Scheme 2). [15][16][17] No 1,2-epoxides of linalool were detected ( 1 H NMR, GC). 8,9 The relative configurations of major isomers of heterocycles 1, 5, and 6 were established by NMR experiments (NOE, HMBC, HM...

The photophysics of two donor-substituted truxenone derivatives has been studied by femtosecond time-resolved transient absorption spectroscopy. The systems consist of a central truxenone acceptor with three triarylamine (TARA) branches which act as electron donors. Upon excitation in the visible regime an electron is transferred from the donor to the acceptor, generating a charge-separated state. This state can be probed via the characteristic absorption of the TARA radical cation around 700 nm. A second absorption band around 420 nm exhibits the same kinetics and is assigned to an absorption of the radical anion of the truxenone moiety. The back electron transfer and the recovery of the ground state can be interpreted within the framework of Marcus theory. To study the dependence of the back electron transfer on the electronic coupling, the distance between the donor and the acceptor was adjusted. Two solvents were employed, dimethylsulfoxide and dichloroethane. A biexponential decay of the bands assigned to the charge-separated state was observed, with time constants in the picosecond range. Surprisingly, the rates for electron back transfer do not follow the simple picture of the donor-acceptor distance being the determining factor. The observations are explained within a model that additionally takes steric interactions between the donor and the acceptor into account.