Mercury(II) chloride-mediated cyclization -: Rearrangement of O-propargylglycolaldehyde dithioacetals to 3-pyranone dithioketals:: An expeditious access to 3-pyranones

O-Propargyl glycolaldehyde dithioacetals undergo a unique cyclization-rearrangement in the presence of mercuric chloride and calcium carbonate to afford 3-pyranones exclusively or along with 2,5-dihydrofuran-3-carboxaldehydes via their dithioketals and dithioacetals.