Dimethyl thiophene-2-malonate

Thermolysis of the ylide (15) in thiophene results in ready rearrangement to dimethyl thiophene-2-malonate (16). The same product is obtained if the thermolysis is carried out in the presence of 2-methylthiophene or cyclohexene, proving that the rearrangement occurs by an intramolecular process (78CC85). However, when 2,5-disubstituted thiophenium ylides are thermolyzed, dissociation to carbenoid species seems to occur. This reaction is further discussed in Section 3.14.2.9. 

Thiophenium ylides. The reaction of dimethyl diazomalonate with thiophene with conventional copper catalysts is extremely slow, but does result in dimethyl thiophene-2-malonate (2) in about 35% yield. When rhodium(II) aceta is used as catalyst, the reaction at 20° is still slow (18 hours), but results in thiophenium bismethoxycarbonylmethylide (1) in 95% yield. This reaction is facilitated by halogen substituents the ylides are not formed from thiophenes substituted with cyano, formyl, or acetyl groups. ... 

Synthetic Uses of Thiophen Derivatives.—The reaction between dimethyl diazo-malonate and thiophen is catalysed by rhodium salts the product is a stable ylide (36) which can be used as an equivalent of bis(methoxycarbonyl)carbene. Thus the heating of (36) with cyclo-octene under reflux affords the bicyclononane (37) in... 

Some functionalized thiophenes have been investigated in order to assess the scope of ylide-derived chemistry. As already mentioned, 2-(hydroxymethyl)thiophene still gives the S-ylide upon Rh2(OAe)4-catalyzed reaction with dimethyl diazomalonate 146 but O/H insertion instead of ylide formation seems to have been observed by other workers (Footnote 4 in Ref. 2S4)). From the room temperature reaction of 2-(aminomethyl)thiophene and dimethyl diazomalonate, however, salt 271 was isolated quite unexpectedly 254). Rh2(OAc)4, perhaps deactivated by the substrate, is useless in terms of the anticipated earbenoid reactions. Formation of a diazo-malonic ester amide and amine-catalyzed cyclization to a 5-hydroxytriazole seem to take place instead. 

The rhodium- or copper-catalyzed interaction of dimethyl diazomalonate with 2-(l-al-kenyl)thiophenes yields either a dimethyl 2-(2-thienyl)cyclopropane-l,l-dicarboxylate, a thiophenium ylide, or a dimethyl [5-(l-alkenyl)-2-thienyl]malonate, depending on the substituents at the alkene bond and the heterocyele. ... 

Oxidatively generated electrophilic malonyl radicals react regiospecifically with thiophene to form (2-thienyl)malonic ester <88H(27)2627>. Treatment of thiophene with cerium(IV) sulfate and an excess of dimethyl malonate in methanol at room temperature yields 2-thienylmalonic ester in 85% yield. In this case, the initially formed cr-radical is oxidized by the cerium(IV) sulfate. 2-Methylthiophene similarly gives the 5-malonyl-substituted product. Benzo[i]thiophene leads to the 2-malonyl-benzo[Z)]thiophene in 41% yield. Monosubstituted malonates could also be used in this reaction. Thiophene and 2-acetylthiophene react with triethyl methanetricarboxylate in the presence of Mn(III) to form the corresponding thienylmethane tricarboxylic esters. Yields are about 55% <91S567>. 

ProIine-derived phosphines bearing various sulfenyl substituents have been developed Use of 21a-g as chiral ligands provided (5)-2, except 21e [(/ )-2], with 31-88% ee in the Pd-catalyzed allylic alkylation of 1 with dimethyl malonate using [Pd(7r-allylX l]2, BSA, and AcONa in dichloromethane at room temperature. Increasing the steric bulk of the substituents of the sulfenyl groups results in enhanced enantiocontrol (21g. provides 88% ee). The thiophene ligand 22 provides (R)-2 with 30% ee (Scheme 12). 

Thiophen Analogues of Quinoline and Related Compounds.—Convenient methods for the synthesis of the thiophen analogues of quinoline have been worked out. By the condensation of 2- and 3-thienylanunonium hexachlorostannates with malonic aldehyde tetraethyl acetal, thieno-[2,3-6]pyridine (538) and thieno[3,2-6]pyridine (539) were obtained in 44% and 77% yields. With other /5-dicarbonyl compotmds, substituted derivatives were obtained. Thus, acetoacetaldehyde dimethyl acetal gave... 

Scheme 83 The reaction of dimethyl malonate anion with carbon disulfide leading to a 3,4-dihydroxythieno[2,3-b]thiophene [130]...

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