Interrelation of thioethers containing conjugated systems with 6π‐electrons: (Base‐catalysed isomerisations in liquid ammonia)

Abstract

The present investigation deals with interrelations between thioethers of the types R¹CH₂CR² = CH ‐C≡CSCH₃ (3‐en‐1‐yne thioethers)R¹CH = C(R²)CHC = CHSCH₃ (1,2,4‐trienyl thioethers)R¹CHC(R²)C≡CCH₂SCH₃ (4‐en‐2‐yne thioethers) andR¹CH₂CR² = C = C=CHSCH₃ (1,2,3‐trienyl thioethers). Under the influence of sodium ethoxide in liquid ammonia all compounds with R¹=H are isomerised quantitatively into 3‐en‐1‐yne thioethers CH₃ − C(R₂)=CH‐C ≡ CSCH₃, whereas the homologues with R¹ = CH₃ are quantitatively converted into a mixture of 1,2,4‐trienyl thioether and 4‐en‐2‐yne thioether. For further details see Table I.Treatment of our substrates with an excess of sodamide in liquid ammonia and subsequent hydrolysis always produces 1,2,4‐trienyl thioethers; 1,2,3‐trienyl thioethers are the presumed intermediates (Tables II‐V).The yields of the sodamide reactions are often rather low because of side‐reactions, among which polymerisation is included. Certain substrates suffer extensive loss of the thioether group by nucleophilic attack at sulfur (see Table II).In Appendix III a simple method for expressing the notation of unsaturated systems is developed; it is useful in drawing conveniently arranged diagrams depicting interrelations.