Acylation of multiple anions of poly-.beta.-ketones by hydroxy- and alkoxybenzoates. Cyclization of the resultant tetraketones to benzophenones and xanthones

Abstract

130-140 °C (0.01 mm); mass spectrum, mje 381, 379, 377 (M+); NMR (CDClg) 0.27 (9 H, s, SnCHg, Jn9Sn_iH = 52 Hz) and 1.42 (CCH3) are associated with the major (7) isomer, while corresponding signals at 0.24 and 1.45 characterize the 6-N02 isomer. Consistent alkyl proton absorption and two regions of aromatic resonance (ca. 7.0-7.42 and 7.9-8.2) are observed. (Some impurities are revealed by the and 13C NMR spectra.) 13C spectra were obtained on the JEOL FX-100 spectrometer at 25.04 MHz. The solvent employed was a mixture (60:40) of deuteriochloroform and dichloromethane, and spectra were referenced to 13CDC13 as 77.00 ppm. 199Hg spectra were obtained on the same spectrometer modified for multinuclear observation. The operating frequency was 17.82 MHz (benzylmercuric chlorides) and 17.83 MHz (dibenzylmercury series). The solvent was again 60:40 CDC13-CH2C12 and 10-mm tubes were used. The chemical shifts are referenced to the (unsubstituted) parent compounds, so that the differences represent the substituent chemical shifts. The variation in shift between the mono-and dibenzyl mercurials is in excess of 400 ppm, and relative to (CH3)2Hg, the shifts can be calculated to be ca.-1120 and -700 ppm, respectively (i.e., upfield). Concentrations of mercurials were very close to 0.4 M, and in most cases, known mixtures of two compounds were examined, and the 199Hg shifts obtained were little different from those when single compounds were examined.Usually a fluoro-substituted benzyl mercurial was a member of the mixture, as this l99Hg resonánce (with 199Hg-19F coupling) could be easily recognized. The dibenzyl mercurials provide sharp spectra, whereas some broadening characterized the spectra of the mercuric chlorides. u9Sn spectra were obtained on the JEOL FX-100 spectrometer at a frequency of 37.70 MHz for solutions 0.5 M in 65:35 CDC13-CH2C12 solvent. Internal tetramethyltin (CH3)4Sn was used as reference, and dilution studies showed very minor concentration effects.

Synthesis of Xanthones: An Overview

“…These include aryl anion addition to salicylaldehyde, followed by reduction to xanthene and eventual oxidation to xanthone (Tanase method) h) [45,46], synthesis of benzophenones involving ketimine intermediates i) (Robinson and Nishikawa synthesis) [47], synthesis from a thioxanthen-9-one-10,10-dioxide nucleus j) [34,48], from extended poly-β-ketides k) [49][50][51], and from the nucleophilic addition of phenols to alkoxycarbonyl-pbenzoquinones (method of Muller and coworkers) followed by reduction l) [52,53]. These general approaches are shown in Scheme 2.…”

Biosynthetic studies using 18O isotope shifts in 13C nuclear magnetic resonance

“…Although these complex patterns initially obscured the small 1 8 0 isotope shifts, we have recently been able to resolve the uncoupled singlets from the superimposed doublets using spin echo Fourier transform techniques (26).4 Presence of acetate-derived oxygens could be detected by isotope shifts at C-1, C-3, C-8, and C-10 of sterigmatocystin 9. Xanthone ring formation must therefore proceed by attack of the oxygen at C-8 on the C-7 position, probably via an addition-elimination process (27) on an unsymmetrical intermediate since the carbon labeling pattern in the phenolic ring is unscrambled (2 1,28). Lack of 1 8 0 label at C-12 is in accord with probable aerobic cleavage of the anthraquinone ring of a versicolorin A type precursor, but the absence of any oxygen functionality at C-5 of sterigmatocystin 9 remains unexpected.…”

Synthesis of Heterocyclic Compounds via Nucleophilic Aroylation Catalyzed by Imidazolidenyl Carbene

“…30) The first one is based on the cyclization of 2-hydroxybenzophenones, [31][32][33] and the second involves the cyclodehydration of o-phenoxybenzoic acids. [34][35][36] Our method is based on the cyclization of 2,2Ј-difluorobenzophenones 5 prepared by NHC-catalyzed aroylation of 3,4-difluoronitrobenzene (3) and fluorobenzaldehydes 4 (Chart 2).…”