1,3-Propanedithiol Bis(p-toluenesulfonate)1

(n = 3)

[3866-79-3]  · C17H20O4S4  · 1,3-Propanedithiol Bis(p-toluenesulfonate)  · (MW 416.65) (n = 2)

[2225-23-2]  · C16H18O4S4  · 1,2-Ethanedithiol Bis(p-toluenesulfonate)  · (MW 402.62)

(dithianylation and dithiolanylation of methylene groups adjacent to carbonyl;2 a,a-dithianyl cycloalkanones undergo oxidative ring scission;3 oxidation of ketones to 1,2-diketones can be achieved by a,a-dithianylation or dithiolanation of ketones followed by hydrolysis4)

Physical Data: 1,3-propanedithiol bis(p-toluenesulfonate): mp 67 °C; 1,2-ethanedithiol bis(p-toluenesulfonate): mp 76 °C.

Preparative Methods: treatment of potassium thiotosylate, itself made by the reaction of p-Toluenesulfonyl Chloride with Potassium Hydrogen Sulfide, with 1,3-dibromopropane or 1,2-dibromoethane in the presence of Potassium Iodide affords 1,3-propanedithiol bis(p-toluenesulfonate) and 1,2-ethanedithiol bis(p-toluenesulfonate), respectively.5

Oxidative Ring Cleavage of Cycloalkanones.

Ketones can be a,a-dithianylated or a,a-dithiolanylated by treatment of their enamines or a-formyl derivatives with 1,3-propanedithiol or 1,2-ethanedithiol bis(p-toluenesulfonate), respectively.1,2 Subjection of a,a-dithianyl ketones to Potassium Hydroxide in t-BuOH results in carbonyl carbon-dithiane carbon bond cleavage, affording o-dithianyl acids (eq 1).3 Presumably, a mechanism similar to the benzilic acid rearrangement is operative. Consistent with this assumption is the observation that easily enolizable and sterically hindered dithianyl ketones are inert to these conditions. The lack of examples of similar cleavage of a,a-dithiolanyl ketones may be related to the inability of dithiolanes to support anion formation.6 Alternative methods for effecting this type of cleavage, such as ozonolysis of an enol derivative, frequently are poorly reproducible.

The exquisite regioselectivity possible in enamine formation or a-formylation of cycloalkanones, followed by a,a-dithianation and ring cleavage, has been exploited in several natural product syntheses (eqs 2-4).7-10

Addition of organometallics to the carbonyl carbon, followed by base cleavage of the resulting a,a-dithianyl carbinols, generates o-dithianyl ketones (eq 5).11

1,2-Carbonyl Transposition and Methylene Protection.

Dithianes and dithiolanes can be removed under hydrolytic or reductive conditions (see 1,3-Propanedithiol and 1,2-Ethanedithiol). As a,a-dithianyl- and dithiolanylation of ketones effects oxidation of the a-carbon, hydrolytic removal of the protecting group affords 1,2-diketones (eq 6).4,12 Chemical modification of the carbonyl carbon before hydrolytic removal of the dithiane or dithiolane effects 1,2-carbonyl transposition (eq 7).13

The ability to convert a dithianyl or dithiolanyl carbon to methylene by treatment with Raney Nickel enables methylene protection a to a carbonyl. For example, the less enolizable a-methylene of a cycloalkanone can be alkylated by the sequence: (a) dithiolanylation of the more enolizable methylene; (b) enolization and alkylation at the remaining methylene; (c) reductive removal of the dithiolane group (eq 8).14

1. Woodward, R. B.; Pachter, I. J.; Scheinbaum, M. L. JOC 1971, 36, 1137.
2. (a) Woodward, R. B.; Pachter, I. J.; Scheinbaum, M. L. OS 1974, 54, 39. (b) Woodward, R. B.; Pachter, I. J.; Scheinbaum, M. L. OS 1974, 54, 37.
3. Marshall, J. A.; Seitz, D. E. JOC 1974, 39, 1814.
4. McMurry, J. E.; Farina, V. TL 1983, 24, 4653.
5. Woodward, R. B.; Pachter, I. J.; Scheinbaum, M. L. OS 1974, 54, 33.
6. Wilson, S. R.; Georgiadis, G. M.; Khatri, H. N.; Bartmess, J. E. JACS 1980, 102, 3577.
7. Takano, S.; Sasaki, M.; Kanno, H. Shishido, K.; Ogasawara, K. JOC 1978, 43, 4169.
8. Takano, S.; Masuda, K.; Ogasawara, K. H 1981, 16, 1509.
9. Honda, T.; Ishizone, H.; Naito, K.; Wakako, M.; Suzuki, Y. CPB 1992, 40, 2031.
10. For other examples, see: (a) Marshall, J. A.; Seitz, D. E. JOC 1975, 40, 534. (b) Kametani, T.; Matsumoto, H.; Nemoto, H.; Fukumoto, K. JACS 1978, 100, 6218. (c) Trost, B. M.; Hiroi, K.; Jungheim, L. N. JOC 1980, 45, 1839.
11. Trost, B. M.; Preckel, M. JACS 1973, 95, 7862.
12. For other examples, see: (a) Bryant, R. J.; McDonald, E. TL 1975, 16, 3841. (b) Dauben, W. G.; Walker, D. M. JOC 1981, 46, 1103.
13. Marshall, J. A.; Roebke, H. JOC 1969, 34, 4188.
14. Chelucci, G.; Cossu, S.; Scano, G.; Soccolini, F. H 1990, 31, 1397.

Peter G. Klimko

Alcon Laboratories, Fort Worth, TX, USA

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