Photo-assisted electron injection at a semiconductor—NH3 interface

Illumination of a p-type semiconductor—NH₃ interface (or heterojunction) with photons of energy greater than the semiconductor band gap causes electrons to be injected into the NH₃. There is no hole injection at a n-type electrode. Suggestions are made for the required energy levels in the liquid.     

Biologically active metabolites from fungi, 19: new isocoumarins and highly substituted benzoic acids from the endophytic fungus, Scytalidium sp

Six known metabolites, two new isocoumarins 4 and 8, and one new highly substituted benzoic acid derivative 9 were isolated from the ethyl acetate culture extract of a fungal endophyte, Scytalidium sp. In addition, another new benzoic acid 10 with an unusual 1,2-dicarbonyl side chain was indirectly identified from its methylated derivatives 10a-10d.     

Determination of the absolute configurations of natural products via density functional theory calculations of vibrational circular dichroism, electronic circular dichroism, and optical rotation: the iridoids plumericin and isoplumericin

The absolute configurations (ACs) of the iridoid natural products, plumericin (1) and isoplumericin (2), have been re-investigated using vibrational circular dichroism (VCD) spectroscopy, electronic circular dichroism (ECD) spectroscopy, and optical rotatory dispersion (ORD). Comparison of DFT calculations of the VCD spectra of 1 and 2 to the experimental VCD spectra of the natural products, (+)-1 and (+)-2, leads unambiguously to the AC (1R,5S,8S,9S,10S)-(+) for both 1 and 2. In contrast, comparison of time-dependent DFT (TDDFT) calculations of the ECD spectra of 1 and 2 to the experimental spectra of (+)-1 and (+)-2 does not permit definitive assignment of their ACs. On the other hand, TDDFT calculations of the ORD of (1R,5S,8S,9S,10S)-1 and -2 over the range of 365-589 nm are in excellent agreement with the experimental data of (+)-1 and (+)-2, confirming the ACs derived from the VCD spectra. Thus, the ACs initially proposed by Albers-Sch?nberg and Schmid are shown to be correct, and the opposite ACs recently derived from the ECD spectra of 1 and 2 by Els?sser et al. are shown to be incorrect. As a result, the ACs of other iridoid natural products obtained by chemical correlation with 1 and 2 are not in need of revision.     

Two Unusual Carbohydrate Reactions: Nucleophilic Ring Opening of an Anhydrosugar and Reductive Elimination with Co‐occurring Hydrogenation

Treatment of the 1,6‐anhydrosugar epoxide 5 with a cyano‐Gilman cuprate [(CuCN (6 eq.), MeLi (12 eq.)] surprisingly led to the open chain rearranged (2S,3R)‐1,2‐dihydroxy‐3,6‐dimethylheptan‐4‐one (7), structurally confirmed by conversion to the corresponding diacetate 8. Another unusual reaction was found by hydrogenation of the 2‐tosyl‐1‐bromosugar 11, leading in one operation to the twofold deoxygenated chiral pyran derivative 14. This procedure might prove to be useful in the rapid deoxygenation of sugar derivatives.     

Communication: Furanoside C-Glycosides from an O-Methyl Pyranoside: An Unexpected ß-Hydroxy-1,3-Dithiane Rearrangement

In the course of our investigations on the synthesis of enantiomerically pure anthracycline antibiotics by incorporation of chiral building blocks we prepared the O-methyl 3-deoxy-2-C-ethylribopyranoside 1.¹ The further synthetic plan required the conversion of 1 to the dithioacetal 2 followed by glycol cleavage to a partially protected 1,4-dialdehyde for coupling experiments to leucoquinizarine in a Marschalk reaction. However, the reaction sequence failed¹ and optically active rhodomycinone had to be synthezised in a different way.² A reinvestigation of the synthesis revealed that the thioacetalization of 1 using the acidic conditions recommended by Corey et al.³ did not yield the usual open chain dithioacetal 2 but rather three new unexpected products. The less polar fraction was identified by ¹H and ¹³C NMR as tetrahydrofuran derivative 3a with the dithiane ring in a ß-orientation. The solid polar fraction (12%) consisted of a nonseparable 1:2.2 mixture of the epimeric deoxygenation products 4/5.     

Synthesis of the Aliphatic Subunit of the Macrolide LL‐Z 1640‐2 via Vasella Ring Opening of a 6‐Iodo‐4‐deoxy‐D‐mannose

The synthesis of the aliphatic subunit 9 of the macrolide LL‐Z1640‐2 (I), starting from a 4‐deoxy‐D‐mannose derivative 2a, is described. The procedure includes the first successful application of a Vasella ring opening reaction for a 4‐deoxypyranoside. Nucleophilic addition of an alkynyllithium reagent to the aldehyde 4 led to the propargylic alcohol 7, which was converted to the advanced building block 9 in two further steps.     

The ν4 fundamental of three isotopic species of CF4

The vibration-rotation spectra of the ν₄ fundamental of ¹²CF₄, ¹³CF₄, and ¹⁴CF₄ have been observed with 0.06 cm^?1 resolution. A least squares fit of the data has been used to evaluate the pertinent molecular constants. The band centers are 631.199, 629.285, and 627.348 cm^?1 for ¹²CF₄, ¹³CF₄, and ¹⁴CF₄, respectively. The Coriolis constant ζ₄ has been estimated for the three isotopes.     

Radial matrix elements of rn for twofold and threefold isotropic simple harmonic oscillators

A generating function for associated Laguerre polynomials and Louck's recursion relations have been employed independently to formulate radial matrix elements of rⁿ for g-fold (g = 2, 3) isotropic simple harmonic oscillators in terms of quantum numbers v and l. This paper gives all relevant matrix elements (vl|rⁿ|v′l′) of rⁿ for n = 1,2, …, 7 and the diagonal element of r⁸. Introduction of the quantities, $\text{V =}\text{1}\text{2}\text{(v + v′ + g)}$ and $\text{L =}\text{1}\text{2}\text{(l + l′ + g ? 2)}$, simplifies the expressions and reveals symmetries and patterns occurring as n increases. Results are compared with those for the one-fold oscillator and sample computer routines have been prepared for numerical evaluation of the matrix elements for g = 1, 2, 3.