Synthesis, Properties, Chemical Reactivity of 1,3-Dithiolane

1,3-Dithiolane is a five-membered sulfur heterocycle comprised of three carbon atoms and two sulfur atoms present at the 1- and 3-positions of the ring.

Physical Properties

The parent 1,3-dithiolane is a liquid with a bp of 183°C and a density of 1.235g/mL at 25°C. It is resistant to both  acid and alkaline hydrolysis as well as to nucleophilic attack.

Synthesis

Condensation of ethane-1,2-dithiol with aldehyde or ketone using perchloric acid adsorbed silica gel (HClO4. SiO2 ) as a catalyst under solvent-free conditions and afforded 2-substituted 1,3-dithiolanes. The same has also  been obtained by condensation of aromatic aldehyde with ethane-1,2-dithiol using a catalytic amount of Brønsted  acidic ionic liquid in very good yields. Praseodymium triflate, a recyclable catalyst, has also been used for chemoselective thioacetalization to obtain 1,3-dithiolanes. A catalytic amount of silica gel and p-toluenesulfonic acid are  also found to be very useful catalysts for the synthesis of 1,3-dithiolanes in very good yields. All these reactions are  depicted in the following diagram.

Aldehydes and ketones undergo condensation with ethane 1,2-dithiol in the presence of Amberlyst-15, bentonite, and metal salts to give 4-substituted 1,3-dithiolanes and spiro-1,3-dithiolanes in good to moderate yields. The  catalysts used are shown on the reaction arrow as depicted in the following scheme.

An alternative route for the construction of 4-substituted 1,3-dithiolane has been developed through condensation of ethylene dibromide with sodium thiosulfate followed by reaction with formaldehyde or acetone in the  presence of HCl.

1,3-Dithiolan-2-one has been prepared in 83% yields by the reaction of ethane-1,2-dithiol with phosgene in ether  at 20°C.

4,4-Dimethyl-1,3-dithiolane-2-thione has been synthesized by the reaction of 2,2-dimethylthiirane with carbon  disulfide under pressure at 80–100°C in the presence of triethylamine as catalyst.

Chemical Reactivity

RING CLEAVAGE REACTIONS

There are numerous reagents reported for the ring opening of the 1,3-dithiolane ring in which some of them  require drastic reaction conditions, noncompatible with some functional groups. Effective reagents generally used  for ring opening of 1,3-dithiolanes to aldehyde or ketone are CuCl2 -adsorbed silica gel, thionyl chloride, P2I4 /Ac2 O,  Amberlyst-15, NBS in acetone or thallium(III) nitrate in methanol, and HgCl2 /CdCO3 . Examples of ring opening of  1,3-dithiolanes are illustrated in the following diagram.

OXIDATIONS

Microbial oxidation of 1,3-dithiolanes afforded 1,3-dithiolane-1-oxides with high enantiomeric excess.

Chemically, 2-phenyl-1,3-dithiolane is oxidized in a diastereoselective manner by t-BuOOH and Cp2 TiCl2  to a  2-phenyl monosulfoxide derivative.

RING TRANSFORMATION REACTION

1,3-Dithiolane on treatment with WCl6  in DMSO afforded dithiin as a ring-expanded product.