Ketene Dimethyl Thioacetal Monoxide1

[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).

Preparative Methods: prepared from glyoxylic acid in six steps.1a A shorter synthesis involving a two-pot reaction sequence has been developed.2

Conjugate Addition Reactions.

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.

1. (a) Herrmann, J. L.; Kieczykowski, G. R.; Romanet, R. F.; Wepplo, P. J.; Schlessinger, R. H. TL 1973, 4711. (b) Herrmann, J. L.; Kieczykowski, G. R.; Romanet, R. F.; Schlessinger, R. H. TL 1973, 4715.
2. Kaya, R.; Beller, N. R. JOC 1981, 46, 196.
3. (a) Ban, Y.; Ohnuma, T.; Seki, K.; Oishi, T. TL 1975, 727. (b) Yoshida, K.; Sakuma, Y.; Ban, Y. H 1987, 25, 47.
4. Ono, N.; Miyake, H.; Tanikaga, R.; Kaji, A. JOC 1982, 47, 5017.
5. Kieczykowski, G. R.; Pogonowski, C. S.; Richman, J. E.; Schlessinger, R. H. JOC 1977, 42, 175.
6. Davis, R.; Untch, K. G. JOC 1979, 44, 3755.

Janice W. Dieter & R. Karl Dieter

Clemson University, SC, USA

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