2-(3-Methylbutoxy)-1,3-benzodithiolane1

(1; R = CH2CH2CHMe2)

[55315-56-5]  · C12H16OS2  · 2-(Methoxyethoxyethoxy)-1,3-benzodithiolane  · (MW 240.42) (2; R = n-C3H7)

[55315-54-3]  · C10H12OS2  · 2-Propoxy-1,3-benzodithiolane  · (MW 212.36) (3; R = n-C4H9)

[55315-55-4]  · C11H14OS2  · 2-Butoxy-1,3-benzodithiolane  · (MW 226.39) (4; R = CH2CH2OCH2CH2OMe)

[131549-15-0]  · C12H16O3S2  · 2-(3-Methylbutoxy)-1,3-benzodithiolane  · (MW 272.42)

(reagent for synthesis of 2-substituted 1,3-benzodithiolanes by substitution of the 2-alkoxy group by various carbon and hetero nucleophiles; 2-lithio-1,3-benzodithiolanes are useful for nucleophilic acylation)

Physical Data: (1) pale yellow oil; bp 120-125 °C/0.1 mmHg. (2) bp 104-106 °C/0.1 mmHg. (3) bp 116-118 °C/0.1 mmHg. (4) bp 152-156 °C/0.5 mmHg.

Preparative Methods: prepared1 by adding dropwise 0.1 L of a solution of Anthranilic Acid (3 M in dioxane) to a gently refluxing solution of Isopentyl Nitrite (0.36 M), 3-methylbutanol (0.60 M) and Carbon Disulfide (0.15 L) in 1,2-dichloroethane (0.8 L). Diazotization of anthranilic acid with isopentyl nitrite generates, beside 1 equiv of 3-methylbutanol, reactive benzyne, which reacts with excess S=C=S to give 1,3-benzodithiole-2-carbene. Reaction of this carbene with 3-methylbutanol, as described by Nakayama,1 gives 2-(3-methylbutoxy)-1,3-benzodithiolane (1) in about 50% yield. This method has been extended to prepare 2-(propoxy)-1,3-benzodithiolanes (2) and 2-(butoxy)-1,3-benzodithiolanes (3), but the yields are poor. Similarly, when a mixture of freshly prepared diazonium-2-carboxylate (from anthranilic acid, 25.7 g),3 2-(2-methoxyethoxy)ethanol (32 mL), CS2 (63 mL), and CH2Cl2 (1.125 L) is allowed to reflux (1.5 h), about 25% yield of 2-[(2-methoxyethoxy)ethoxy]-1,3-benzothiole (4) can be obtained readily.2

Handling, Storage, and Precautions: dithiolane (1) is a stable and easy to handle material at ambient temperature. Thermally, it is unstable, undergoing substantial decomposition during distillation to give mainly 2,2-bi(1,3-benzodithiolylidene).4a Use in a fume hood.

Introduction.

2-(3-Methylbutoxy)-1,3-benzodithiolane (1) and other related dithio orthoesters, upon treatment with acetic acid at rt, undergo smooth ionization to generate in situ the resonance-stabilized carbocation intermediate 1,3-benzodithiolium ion (5).4b Indeed, the propensity to form this 10p-electron aromatic system (i.e. 5) is so great that treatment of (1) with either 42% Tetrafluoroboric Acid5 or trityl fluoroborate,6 can be employed to obtain 1,3-benzodithiolium fluoroborate in yields in excess of 95%. Thus (1) has become a convenient precursor for the 1,3-benzodithiolium ion (5) (eq 1).

Reactions with Nucleophilic Reagents.

Dithiolane (1) reacts with nucleophiles, such as N,N-dialkylarylamines,4b polymethoxybenzene,4b aliphatic and aromatic thiols,7a activated methylene compounds,7b indole and pyrrole,7c and Grignard reagents, (64-89%)7d-f in a predictable manner to give a variety of 2-substituted 1,3-benzodithioles. While (1) is unreactive towards phenylethynylmagnesium bromide, the dithio orthoester (4) having a chelating group gave the 2-phenylethynyl-1,3-benzodithiole in 55% yield.2

1,3-Benzodithiolane Anions as Nucleophilic Acylation Reagents.7f,8

The 2-alkyl-1,3-benzodithiolanes are readily lithiated with n-Butyllithium in THF at -30 °C and the resulting anions may be alkylated with alkyl halides to give 2,2-dialkyl-1,3-benzodithiolanes.8 This procedure for nucleophilic acylation is completed by hydrolysis to liberate the dialkyl ketones.

Alternatively, the intermediate anion may be efficiently coupled to branched organoboranes, producing hindered ketones or tertiary alcohols by one or two boron-carbon alkyl migrations, as shown in eq 2.7f

Reaction with Aqueous Chlorine.

Treatment of (1) with aqueous chlorine at or around 0-5 °C gives a highly useful compound, 1,2-benzenedisulfonyl dichloride,9 in 90-95% yield.

Related Reagents.

1,3-Benzodithiol-1-ium Tetrafluoroborate; 1,3-Dithiane; 2-Lithio-1,3-dithiane; 1,1,3,3-Tetramethylbutyl Isocyanide.


1. Nakayama, J. S 1975, 38.
2. Houghton, R. P.; Dunlop, J. E. SC 1990, 2387.
3. Logullo, F. M.; Seitz, A. H.; Friedman, L. OS 1968, 48, 12.
4. (a) Nakayama, J. S 1975, 168. (b) Nakayama, J. S 1975, 170.
5. Nakayama, J.; Fujiwara, K.; Hoshino, M. BCJ 1976, 49, 3567.
6. Nakayama, J.; Fujiwara, K.; Hoshino, M. CL 1977, 127.
7. (a) Nakayama, J. S 1975, 436. (b) Nakayama, J. JCS(P1) 1976, 540. (c) Nakayama, J.; Imura, M.; Hoshino, M. BCJ 1980, 53, 1661. (d) Ncube, S.; Pelter, A.; Smith, K. TL 1977, 255. (e) Hughes, R. J.; Ncube, S.; Pelter, A.; Smith, K.; Negishi, E.; Yoshida, T. JCS(P1) 1977, 1172. (f) Ncube, S.; Pelter, A.; Smith, K. TL 1979, 1893, 1895.
8. Ncube, S.; Pelter, A.; Smith, K.; Blatcher, P.; Warren, S. TL 1978, 2345, 2349.
9. Barbero, M.; Degani, I.; Fochi, R.; Regondi, V. G 1986, 116, 165.

Acharan S. Narula & Kishore Ramachandran

University of North Carolina, Chapel Hill, NC, USA



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