[937-63-3] · C8H7ClOS · O-p-Tolyl Chlorothioformate · (MW 186.67)
Physical Data: bp 52-53 °C; d 1.21 g cm-3.
Solubility: sol most common organic solvents.
Form Supplied in: commercially available as liquid (97% pure).
Analysis of Reagent Purity: GC.
Handling, Storage, and Precautions: moisture sensitive; keep cold; corrosive; toxic; use in a fume hood.
Formation of thiocarbonate O-esters from sterically hindered alcohols, followed by pyrolysis, provides an alternative to the Chugaev reaction in the synthesis of alkenes. In the examples shown in eqs 1 and 2, pyrolysis of the corresponding xanthates gives lower yields.1,2
The pyrolysis of thiocarbonate O-esters has been utilized in the synthesis of several natural products. In an approach to the synthesis of (-)-acorenone (eq 3), pyrolysis of the xanthate gives consistently low yields.3 The favored pathway appears to be conversion to the dithiol carbonate. Alternatively, conversion to the thiocarbonate O-ester and subsequent pyrolysis gives the desired alkene in 68% yield. This methodology has also been successfully used in a total synthesis of (±)-silphenene (eq 4).4 Ordinary dehydration conditions lead to retroaldolization, while pyrolysis of the thiocarbonate O-ester gives the desired enone in 84% yield. An intermediate in the total synthesis of (-)-hibaene has been prepared by pyrolysis of the respective monothiocarbonate O-esters of both epimeric diols (eq 5).5
Thiocarbonate esters of alcohols can be deoxygenated using the Barton-McCombie procedure.6 Several examples of this deoxygenation methodology in the synthesis of deoxyribose nucleosides have been cited (eq 6).7-9
[Heteroaryl(hydroxy)methyl]phosphonates are readily converted to O,O-thiocarbonates on treatment with O-p-tolyl chlorothioformate in MeCN/DMAP, while the reaction in pyridine/CH2Cl2 affords the isomeric O,S-thiocarbonates (eq 7).10 Homolytic cleavage with Tri-n-butylstannane/Azobisisobutyronitrile provides a convenient approach to dialkyl heteroarylmethylphosphonates.
Judi A. McKinney
Tularik, South San Francisco, CA, USA