Protonation, and reductive cleavage by lithium of the CS bond, in (methylthio)pentadienylic anions generated from various cis,trans‐isomers of 1‐(methylthio)‐1,3‐pentadiene and 1‐(methylthio)‐1,4‐pentadiene

Abstract

AbstractTreatment of the various cis,trans‐isomers of CH3SCHCHCHCHCH3 and CH3SCHCHCH2CHCH2 with a slight excess of potassium amide in liquid ammonia, followed by quenching of the solutions thus obtained with ammonium chloride, gives, in all cases, the is isomer CH3SCH2CHCHCHCH2(> 90% trans) From the anionic solutions 1H NMR spectra have been recorded.Reductive cleavage of the CS bond of the anions CH3SCHCHCHCHCH2⊖ with lithium in liquid ammonia, followed by methylation, leads to almost complete recovery of CH3SCHCHCHCHCH3. During this cleavage, the double bond next to sulfur retains its configuration, while the configuration of the other double bond changes from trans to cis. It remains the same, however, on starting from a (methylthio)pentadiene with a cisC3C4 double bond. The ultimate result of the cleavage procedure with CH3SCHCHCH2CHCH2 is CH3SCHCHCHCHCH3: the configuration of the C1C2 double bond remains the same and the C3C4 double bond is always cis.