[111674-84-1] · C4H8OS2 · Ketene Dimethyl Thioacetal Monoxide · (MW 136.26)
(formylmethyl synthon used as an acceptor in conjugate addition reactions1)
Alternate Names: ketene bis(methylthio)acetal monoxide; 1-(methylsulfinyl)-1-methylthioethylene.
Physical Data: yellow liquid; bp 145-150 °C/27 mmHg; 1H NMR (CDCl3) d 2.38 (3H, s), 2.64 (3H, s), 5.51 (1H, d, J = 2 Hz), 6.01 (1H, d, J = 2 Hz); IR (neat) 3490, 1593, 1429, 1330, 1070, 970, 893 cm-1; MS (70 eV), m/e (rel. intensity) 136 (5.9, M+), 126 (0.8), 120 (1.6), 108 (3.2), 90 (8.4), 73 (100.0), 58 (15.1).2
Solubility: sol most common organic solvents (i.e. THF, Et2O, DME, CH2Cl2, MeCN, t-BuOH, CS2, benzene).
The reagent functions as a two-carbon acceptor in Michael reactions with a variety of sodium enolates of b-dicarbonyl compounds (i.e. b-keto esters (eq 1),1 malonates,1 and b-diketones1), and in conjugate addition reactions with lithium enolates of simple carbonyl compounds (i.e. ketones,3a esters (eq 2),1 a,b-enoates (eq 3),1 and a-methylthio esters1), and enamines.1 The reagent provides for umpolung reactivity since hydrolysis of the dithioacetal monoxide affords a 1,4-disposition of carbonyl functionality rather than the 1,5-disposition obtained in the Michael reaction.
The synthesis of oxygenated Aspidosperma alkaloids involves addition of a tetracyclic nine-membered ring lactam enolate to CH2=C(SOMe)SMe (eq 4).3b Conjugate additions of nitroalkanes proceed quantitatively when 1,8-Diazabicyclo[5.4.0]undec-7-ene is used as the base.4 Syntheses of the natural products (±)-prostaglandin F2a5,6 and (±)-1-acetylaspidoalbidine3a employ this particular methodology as a key step.
Janice W. Dieter & R. Karl Dieter
Clemson University, SC, USA