Chemistry of acetylenic ethers 82: On the different influence of alkylthio and alkoxy groups on the course of 1,4‐Eliminations

Abstract

Abstract 1,4‐Elimination of alkanethiols RSH from the bis‐thioethers RSCH 2 CCC;H 2 SR with sodium ethoxide in liquid ammonia at −33°, affords two products viz. enynyl thioethers CH 2 CHC≡CSR and dienyl‐bis‐thioethers CH 2 CH‐C(SR)CHSR resulting from readdition of thiolate. Experimental evidence for the occurrence of cumulenyl thioethers CH 2 CCCHSR as intermediates in these elimination reactions is described. Reaction of the “mixed” compounds RSCH 2 C≡CCH 2 OR′, RSCH 2 C≡CCH(CH 3 )OR′ and RSCH 2 C≡C‐C(CH 3 ) 2 OR′ with sodium ethoxide at −33° in liquid ammonia results in an elimination of the OR′ [R′ = alkyl or ‐CH(CH 3 )OC 2 H 5 ] group and formation respectively of the enynyl thioethers RSC≡CCHCH 2 , RSC≡CCHCHCH 3 and a mixture of RSC≡CCHC(CH 3 ) 2 and the carbinol RSCH≡C(OH)(CH 3 )] = CCH–C The carbinol can also be obtained by reaction of RSCHCCHC(CH 3 ) = CH 2 with lithium amide and acetaldehyde.