Synthesis, structure and reactivity of some chiral benzylthio alcohols, 1,3-oxathiolanes and their S-oxides

A series of amino acid-derived chiral benzylthio alcohols have been prepared and characterised. A chiral mercapto alcohol derived from S-leucine has been used to form three chiral 2,4-disubstituted 1,3-oxathiolanes. One of these has been oxidised to the S-oxide and another to the S,S-dioxide. The cis and trans isomers have been characterised by ¹H NMR in each case and it appears that thermal epimerisation at C-2 is possible at the sulfoxide oxidation state. The X-ray structure of major trans diastereomer of 2-phenyl-4-isobutyl-1,3-oxathiolane S,S-dioxide shows an envelope conformation with oxygen at the flap and an internal angle at sulfur of just 93.8°. This compound fragments upon flash vacuum pyrolysis at 700 °C to give SO₂, benzaldehyde and 4-methylpent-1-ene.