[43228-10-0] · C5H8O2S · Methyl 2-Methylthioacrylate · (MW 132.20)
(versatile and reactive Michael acceptor2-5)
Physical Data: bp 78 °C/12 mmHg.
Solubility: sol Et2O, THF, EtOH, and most organic solvents.
Analysis of Reagent Purity: IR, NMR, GLC.
Preparative Methods: prepared either by the reaction of methyl 2-chloroacrylate1a or methyl 2-bromoacrylate1b with Methanethiol in the presence of Triethylamine and N,N-Dimethylformamide. It is also obtained1c quantitatively by chlorination of methyl 2-alkylthiopropionates (alkyl = Me/Et) with Sulfuryl Chloride at 0 °C followed by dehydrochlorination using refluxing chloroform. For preparation of alkyl 2-alkylsulfonylacrylates and its uses, see Gipstein.8
Handling, Storage, and Precautions: since the reagent is an acrylate, it should be stored under N2 in the refrigerator and should be inhibited with ionol or 100 ppm of hydroquinone monomethyl ether. Use in a fume hood.
Lithium enolates derived from esters,2a lactones,2a and thioacetal monosulfoxide2b undergo smooth Michael addition in high yield. These adducts on hydrolysis give the corresponding carbonyl analogs (eqs 1-3). Enamines2a give high yields of Michael adducts (eq 4).
The lithium enolate of a lactam undergoes Michael addition to methyl 2-methylthioacrylate at -78 °C, furnishing 98% yield of the adduct (eq 5) which was later converted to (±)-vincamine alkaloid. A similar Michael addition was used in the synthesis of a-kainic acid (eq 6).4
The reagent undergoes a facile, Aluminum Chloride-catalyzed Diels-Alder5a reaction with Isoprene, Cyclopentadiene, and cyclohexadiene and gives [4 + 2] addition products (eqs 7 and 8). If the reaction is carried out under thermal conditions, mixtures of endo and exo adducts are formed. These adducts are converted to ketones using N-Chlorosuccinimide/t-butanol.
This further demonstrates that methyl 2-methylthioacrylate can be regarded as a ketene5b equivalent. With electron-poor dienes such as 3-aryl-1,2,4,5-tetrazine,6 it gives regioselectively only one of two possible [4 + 2] cycloadducts (eq 9).
Use of this reagent in the acid-catalyzed ene reaction7 does not give any ene product; instead, it rearranges to trans-b-(methylthio)acrylate (eq 10).
Anubhav P. S. Narula
International Flavors & Fragrances, Union Beach, NJ, USA