[540-63-6] · C2H6S2 · 1,2-Ethanedithiol · (MW 94.20)
(1,3-dithiolane formation; ether cleavage; reduction (carbonyl to methylene; sulfoxide to thioether); gem-difluoride formation; dithiolenium ion formation)
Physical Data: d 1.123 g cm-3 (23.5 °C); bp 146 °C/760 mmHg; 63 °C/46 mmHg.
Solubility: slightly sol water; miscible with many organic solvents.
Form Supplied in: widely available.
Handling, Storage, and Precautions: stench! Inhalation can cause chest pain, headache, nausea, pulmonary edema; LD50 (oral, mouse) 342 mg kg-1; see 1,3-Propanedithiol. Use in a fume hood.
1,2-Ethanedithiol (1) condenses with aldehydes, ketones, and acetals to afford 1,3-dithiolanes,1,2 useful for carbonyl protection (eqs 1 and 2).3a,b Stability, condensation selectivity, and conditions for carbonyl regeneration parallel those discussed for 1,3-Propanedithiol.4 Esters and lactones can be protected as ketene dithioacetals and/or dithioortholactones, resistant to nucleophilic attack, using the bis(dimethylalanyl) derivative of (1).5
An acetonide can be cleaved in the presence of a nearby t-butyldiphenylsilyl ether with (1).6a Under more vigorous conditions, aliphatic methyl ethers are cleaved (eq 3).6b
Raney Nickel desulfurization of 1,3-dithiolanes effects overall reduction of C=O to CH2, as does Sodium-Ammonia in THF (eqs 4 and 5).7a,b Na/hydrazine is an alternative reagent (eq 6).10a Peptidic sulfoxides are reduced to thioethers with (1) and an electrophilic catalyst.11a
1,3-Dithiolanes yield geminal difluorides on treatment with Pyridinium Poly(hydrogen fluoride) and a mild oxidant (eq 7).8a,b 1,3-Dithianes react more slowly and give lower yields.8a
Acid chlorides, anhydrides, esters, and orthoesters, upon treatment with (1) and a Lewis acid, can produce electrophilic 1,3-dithiolenium cations which react with a variety of carbon nucleophiles.9 Selective indole formylation in the presence of a primary carboxamide could thus be achieved (eq 8).9a
Racemic ketones have been resolved by condensation with (R,R)- or (S,S)-2,3-butanedithiol, then reduced as above to give resolved deoxy compounds (eq 6).10a,b Oxidation of prochiral 1,3-dithiolanes under modified Katsuki-Sharpless conditions yields monosulfoxides of high ee.10c In peptide synthesis, (1) is frequently used as a cation scavenger during deprotection.11a,b Transition metal cations are strongly chelated by (1), as exemplified by demetalation of CuII and NiII metalloporphyrins.11c
Raymond E. Conrow
Alcon Laboratories, Fort Worth, TX, USA