2-Benzothiazolyl Propargyl Sulfides: Versatile Precursors for Enantiopure Allenes, E-α,β-Unsaturated Ketones and Z-Sulfonylalkenes
22 September 2010 (eFirst)
A novel, stereospecific route to allenes is described. The approach proceeds via a retro-ene reaction, initiated by lithium aluminium hydride mediated cleavage of benzothiazole from the respective (chiral) 2-benzothiazolyl propargyl sulfone precursors. As such, allenes in up to 92% yield are formed under evolution of sulfur dioxide at ambient temperature. Furthermore, a new and mild way to generate E-α,β-unsaturated ketones has been discovered. These substrates are formed in around 50% yield by treating 2-benzothiazolyl propargyl sulfides with hydrogen peroxide and a catalytic amount of ammonium molybdate at room temperature. In the course of this research it was also found that treatment of 2-benzothiazolyl propargyl sulfones with sodium borohydride led to reduction of the triple bond exclusively to the Z-double bond.
allenes - α,β-unsaturated ketones - oxidations - rearrangements - sulfones