SONOGASHIRA COUPLING ROUTES TO ortho-ALKYNYL- AND FUSED-RING SYDNONES
Weisner, Andrew J. M.S., Department of Chemistry, Wright State University, 2003. Sonogashira Coupling Routes to ortho-Alkynyl- and Fused-Ring Sydnones. In the present work, suitably functionalized arylsydnones were used to synthesize a variety of ortho-alkynyl sydnones both as potential precursors to novel sydnoquinolines and to provide non-linear optical (NLO) species of interest to Wright-Patterson Air Force Base (WPAFB). The versatile intermediate, 3-(2-(trimethylsilylethynyl)phenyl)sydnone, was prepared in good yield by the coupling of 3-(2-iodophenyl)sydnone with trimethylsilyl acetylene under Sonogashira conditions. From this intermediate, several ortho-alkynyl sydnones were prepared via a one-pot desilylation with tetrabutylammonium fluoride and Sonogashira coupling with para-substituted aryl iodides. In addition, a three-reaction-in-one-pot procedure was developed to access some of these species directly from 3-(2- iodophenyl)-sydnone. Subsequent reaction of these species with electrophiles has been examined as an avenue to novel sydnoquinolines. For example, there is evidence that the electrophile phenylselenyl chloride has induced cyclization of 3-(2- (phenylethynyl)phenyl)sydnone and 3-(2-(4-methoxyphenylethynyl)phenyl)sydnone in moderate yield. Similarly, concentrated sulfuric acid has effected cyclization of 3-(2- (phenylethynyl)phenyl)sydnone and 3-(2-(4-bromophenylethynyl)phenyl)sydnone, also in low yield. In contrast, trifluoroacetic acid and trifluoromethanesulfonic acid transform these species into novel cinnolines, presumably via sydnone ring cleavage followed by acid-induced cyclization. Sonogashira coupling routes were used to add additional para-alkynylphenyl moieties to the above-mentioned ortho-alkynyl sydnones and generate oligomeric alkynyl sydnones. The aim of this endeavor was to fulfill an interest of the United States Air Force in these species as ligands for the preparation of platinum-centered NLO materials. 3-(2-Ethynylphenyl)sydnone was synthesized from 3-phenylsydnone in a three-step process with an overall yield of 27% to analytically pure material. Similarly, 3-(2-(4- ethynylphenyl-ethynyl)phenyl)sydnone, was synthesized in seven steps at an overall yield of 21%, and 3-(2-(4-(4-ethynyl)phenylethynyl)phenylethynyl)phenyl)sydnone was synthesized in ten steps at an overall 11% yield. A great aid to obtaining these relatively high overall yields was the ability to perform multiple steps of the syntheses in one pot (e.g. three reactions in one pot) at certain points en route. Finally, the above oligomeric alkynyl sydnones were converted into the corresponding 3,4-dicarbomethoxypyrazoles (potential NLO monomers) in moderate to good yield by 1,3-dipolar cycloaddition with dimethylacetylene dicarboxylate.
School:Wright State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:sydnone alkyne palladium catalyzed coupling sonogashira organic chemistry mesoionic
Date of Publication:01/01/2003