Communications
ADVANCED MATERIALSall of the CC1, was added to the working electrode side of the deposition cell. Current density for deposition was typically 2.5-5 mA/cm* and the galvanostatic depositions were carried out for 30-60 min.Scanning electron microscopy @EM) images were obtained using a Cambridge 360 SEM operating at 20 kV in secondary electron imaging mode. For the transmission electron microscopy (TEM) measurements, fibers were electrodeposited directly onto Cu mini grids. Bright field images and diffraction patterns were obtained using a Philips CM30 TEM operating at 300 kV accelerating voltage.X-ray photoelectron spectroscopic (XPS) measurements were made with a Perkin-Elmer model PHI 5100 spectrometer, using Mg-K, radiation. The X-rays were generated at 15 kV, 300 W, with the detector set at a take-off angle of 45". The sample was not sputtered prior to data collection.Raman spectroscopy was performed with a 488 nm laser (10 mW at the sample), and a single spectrograph (ISA 640) coupled to a 512 channel CCD detector (Photometrics PM512). A holographic band reject filter (Kaiser, OD = 6 at 488 nm) between the sample and spectrograph reduced elastic scatter. Integration times were 10-60 seconds, and no change in the spectrum was observed with repeated acquisition. 380" back-scattered geometry with a common focusing and collection lens was employed.
Addition of carbon nucleophiles to (benzocyclobutenedione)tricarbonylchromium(0) (4) results in the formation of exo mono‐ and diadducts as well as 1,2‐diketones as the consequence of proximal ring‐opening reactions. In one case the unexpected formation of benzocycloheptenedione complexes is observed. Treatment of 4 with an excess of 1‐ethoxy‐1‐lithioethene gives the product of a dianionic oxy‐Cope rearrangement followed by an intramolecular aldol addition. This is also the case with lithiated methoxyallene, and as the result the first head‐to‐head coupling product 12 of two methoxyallene molecules is isolated in good yield. 12 is used as a diene in Diels‐Alder cycloadditions, and its molecular structure is compared to that of the similar molecule 13, lacking the two exo methylene substitutents.
Lithiated heterocycles and phenyllithium were tested as alkenyllithium components in the dianionic oxy‐Cope rearrangement taking place upon their addition to (η6‐benzocyclobutenedione)tricarbonylchromium (1). It was found that, with 5‐lithio‐2,3‐dihydrofuran, the rearrangement and subsequent intramolecular aldol addition takes place diastereoselectively. Treatment of 1 with phenyllithium, 2‐lithio‐N‐methylpyrrole, 2‐lithiofuran, or 2‐lithiothiophene, however, resulted only in the formation of single adducts and proximally or distally ring‐opened diadducts, presumably because of the activation energy required to negate the aromatic character of two added anions. When, therefore, the monovinyl adduct rac‐19 was used as starting material, addition both of 2‐lithiofuran and of 2‐lithiothiophene resulted in the desired dianionic oxy‐Cope rearrangements, followed by intramolecular aldol addition. Remarkably, the intramolecular aldol addition takes place with complete regioselectivity, meaning that the bis(enolate) hydrolysis is regioselective. This is explained by a chelate stabilization of one enolate moiety in preference to the other one, hydrolysis of which is thus highly favored.
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