Aryl derivatives elimination reactions

A novel one-pot synthesis of various fused lactones has been achieved via a domino sequence of Knoevenagel/ hetero-Diels-Alder/elimination reactions of N- and 0-prenyl aryl aldehyde derivatives with Meldrum s acid in the presence of D- or L-proline with high diastereoselectivity (Scheme 68) <2005MI1353>. 

The parent system is prepared by oxidation of tetrahydrothiopyran with triphenylmethane and perchloric acid (66HCA2046) in high yield, and the method is applicable to the preparation of virtually all simple alkyl or aryl derivatives. In more complex cases, especially where the strong acid might cause elimination or isomerization side reactions, triphenylmethyl tetrafluoroborate may be used with the thiin precursor (equation 113) (78CL723). 

A simple procedure to prepare 5-aryl- and 5-pyridyl-2-furaldehydes from inexpensive, commercially available 2-furaldehyde diethyl acetal was reported. The reaction proceeded in a four-step, one-pot procedure and the yield of coupling step was usually between 58-91% <02OL375>. A facile route to 3,4-furandicarboxylic acids was developed. DDQ-oxidation of 2,5-dihydrofuran derivatives, which were produced from dimethyl maleic anhydride, furnished the desired esters of furan-3,4-dicarboxylic acid <02S1010>. The furan-fused tetracyclic core of halenaquinol and halenaquinone possessing antibiotic, cardiotonic, and protein tyrosine kinase inhibitory activities was synthesized. Intramolecular cycloaddition of an o-quinodimethane with furan gave the adduct as a single isomer via an enrfo-transition state, which was converted to trisubstituted furan by oxidation-elimination reactions <02T6097>. 

Several of the trialkylaluminum and alkylaluminum halides and hydrides mentioned above are commercially available. Alkynyl, alkenyl, cyclopentadienyl, and aryl derivatives are, in general, not commercially available and must be synthesized for laboratory use. Alkynyl derivatives can be prepared by salt metathesis, as in the reaction of Et2AlCl with NaC=CEt to give Et2AlC=CEt. The acidity of terminal alkynes is sufficient for preparation of alkynyl aluminum compounds by alkane or hydrogen elimination upon reaction with a trialkylaluminum or an aluminum hydride (equation 17), respectively. TriaUcynyl aluminum compounds are typically isolated as Lewis base adducts to stabilize them against otherwise facile polymerization. Alkenyl compounds of aluminnm have similarly been prepared. 

Here we discuss new types d cellulose derivatives synthesized by nucleophilic substitution of mixed polysaccharides containing repeating units of 2,3- and 3,6-anhydro sugars, units d amino sugars, their N-alkyl(aryl)- and N-carboxylalkyl(aryl) derivatives, alkyl derivatives and phenylbarenyl derivatives d deoxygliux)se, elimination reactions of unsaturated derivatives containing multiple C-C bonds in the... 

However, upon photolysis and thermolysis of azidofor-mates (RO-CO-N3, R=alkyl, aryl), the major reaction path is the formation of products derived from capture of the nitrenes (RO—CO—115-119 Carbethoxynitrene (21) has been studied most extensively. This nitrene has been generated by thermolysis and photolysis of 20ii H and by a-elimination of an arysulfonate ion from N-(p-nitrobenzenesulfonyloxy) urethane. 

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