The reaction of (2‐thienyl)acetaldehyde diethylacetal with alkali metal bases

Abstract

Our initial investigations employed the 1, 3-dioxolane (2) and acetal (3) moieties as carbonyl blocking groups during n-butyllithium metalations of the heterocyclic nuclei o f thiophene and furan. Subsequently we became interested in the production of multiple anions from a hetcrocyclic substrate containing a "blocked" carbonyl group. Consequently, c~-(2-thienyl)acetaldehyde diethylacetal (I) with active hydrogens a t positions a and b was selected for reaction with n-butyllithium.ht1t.n treated with n-butyllithium 1 did not provide a stable didnion but instead was found t o undergo a unique elimination-substitution reaction. Treatment of the generated anion with an appropriate electrophile, trimethylchlorosilane or phenyldimethylchlorosilane, resulted in the production of [5-(trimethylsilyl)-2-thienyl]-P-vinylethyl ether (2) and [ 5-(phenyldimethylsilyl)-2-thienyl] -0vinylethyl ether (3) (Scheme I), respectively. Decomposition of the intermediate anion with water provided 78% of 2-thienyl-/.l-vinylethyI ether (4). 1 4Thus it is apparent that metalation provides for dianiorr formation which gives rise concomitantly or otherwise, t o both elimination and substitution products, where the elimination product is a result of the loss of ethoxide ion. Such was verified by the isolation of trimethylethoxysilane and phenyldimethylethoxysilane when a n excess of the electrophilic reagents trimethylchlorosilane and phenyldimethylchlorosilane, respectively, were employed.Although our previous experimental results (2,3) would indicate ring substitution in the 5-thienyl position, this was shown unequivocally to be the case by an unambiguous synthetic route (Scheme I1 and 111).

Mechanistic Investigations on the Photoisomerization Reactions of Five-Membered Ring Heterocyclic Molecules Containing Sulfur and Selenium Atoms

“…Because the selenium element has a larger atomic size in comparison with oxygen and sulfur, molecules including the selenium atom always give an increased polarizability, which, in turn, make them generally less stable than the sulfur analogues. In addition, its physical properties make selenium-containing heterocycles desirable materials in the growth of organooptic and organoelectronic materials. − As a result, because 1,2,3-selenadiazoles undergo a wide variety of reactions as 1,3-dipoles and develop the synthesis of different organoselenium compounds, 1,2,3-selenadiazoles have also attracted much attention in several laboratories. , In fact, because of the reason that 1,2,3-selenadiazoles are easily separated with the loss of a nitrogen molecule and a selenium atom under both light irradiation and thermal conditions, 1,2,3-selenadiazoles have drawn attention as versatile intermediates for the preparation of alkynes. − …”

“…To the best of our knowledge, so far, there has been neither experimental nor theoretical study for the photochemical mechanisms of both 1 and 6 . It is astonishing how little is known about the mechanisms of the photochemical reactions of 1 and 6 because these molecules are so important in bioorganic and organic chemistry. − Accordingly, using a more sophisticated quantum chemical theory, the study of the potential energy surfaces of 1,2,3-thiadiazole ( 1 ) and 1,2,3-thiadiazole ( 6 ) systems is undertaken. The goal of this study is to combine both observed experimental works and theoretical examinations to provide a comprehensive understanding of the excited-state behaviors of 1,2,3-thiadiazoles and 1,2,3-selenadiazoles.…”