Sonogashira Cross-Couplings of Ynamides. Syntheses of Urethane- and Sulfonamide-Terminated Conjugated Phenylacetylenic Systems

Abstract

[reaction: see text] The first successful Sonogashira coupling of ynamides with aryl and vinyl iodides is described here. This study resolves the problem of the competing pathway involving homocoupling of ynamides and provides a practical entry to novel urethane- or sulfonamide-terminated conjugated acetylenic systems. An interesting tandem hydrohalogenation and Sonogashira coupling was also observed to give an en-ynamide.

A Novel Synthetic Approach to Diaminoacetylenes: Structural Characterization and Reactivity of Aromatic and Aliphatic Ynediamines

“…In both molecules, the N-C-C-N axes are close to linearity with C-C-N angles of 174.10(9)8/176.28(9)8 in 3 a and 177.87(14)8/ 173.92(14) in 3 c. The C1 À C2 bond lengths are 1.1992 (12) in 3 a and 1.206(2) in 3 c, in agreement with the presence of C À C triple bonds; a similar, albeit slightly shorter C À C bond length of 1.189(5) was recently reported for an ortho-anisyl-substituted ynamide, which also displays an orthogonal conformation in the solid state. [26] During the formation of 3 a from the reaction 2 a with nBuLi in toluene, we were able to isolate a minor byproduct in approximately 3 % yield, which was identified as 2-(N'-methyl-N'-phenylamino)-N-methylindole (4) by comparison of its NMR spectroscopic data with those reported in the literature (Scheme 3). [27] The yield of 4 increased to 54 % if the lithiation reaction was performed in tetrahydrofuran (THF) or if coordinating additives such as N,N,N',N'-tetramethylethylenediamine (tmeda) were added to the toluene solution prior to the addition of nBuLi.…”

Synthesis of conjugated multi-ynamides by copper-catalyzed reactions

“…In order to overcome this problem, we tested a double Sonogashira coupling between 2,5-dibromothiophene with ynamide 9 14 following the conditions described by Hsung and coworkers for such couplings. 15 Once again, this attempt did not lead to the expected ynamide. We thus decided to try Evano's method to access the target compound.…”

Terminal ynamides: synthesis, coupling reactions, and additions to common electrophiles

“…44 They used Pd(PPh 3 ) 4 as catalyst and CuI or CuCN as cocatalyst to affect smooth transmetallation with aryl iodides at room temperature (Scheme 23). The coupling products 89a – d were obtained with varying yields and the screening of the copper source is apparently important.…”