[102555-71-5]  · C20H14S2  · 1,1-Binaphthalene-2,2-dithiol  · (MW 318.45) (-)

[124414-36-4] (±)


(reagent for the preparation of chiral, atropisomeric organosulfur reagents of C2 symmetry;1 used as chiral ligand and in the preparation of chiral crown ethers)

Physical Data: mp 150-151 °C (benzene); (R)-(-): [a]22D -85.9°; [a]22546 -103.8° (c = 1, CHCl3).

Analysis of Reagent Purity: the presence of the disulfide can be checked by TLC on silica gel, eluting with dichloromethane.

Preparative Methods: the original procedure used Ullman coupling of 1-bromo-2-naphthalenesulfonic acid.2a The intermediate 1,1-binaphthalene-2,2-sulfonic acid can be resolved with strychnine.2b Lithiation of 2,2-dibromo-1,1-binaphthalene with t-butyllithium, quenching with sulfur,2c and reduction of the resulting disulfide is an alternative preparation of the racemic dithiol. More practical procedures entail Newman-Kwart rearrangement of the thioester derived from binaphthol and dimethylthiocarbamoyl chloride, followed by hydrolysis.3-5 Use of enantiomerically pure binaphthol as starting material gives the enantiomerically pure reagent.4 Another resolution procedure involves enantioselective oxidation of sulfides which can be further transformed into the dithiol.6

Handling, Storage, and Precautions: the reagent oxidizes easily to the disulfide and should be stored under inert atmosphere. Use in a fume hood.

Binaphthalene-2,2-dithiol is the starting material for the preparation of a number of sulfur-containing heterocycles of synthetic utility. The basic principle lies in the generation of C2 symmetric chiral variants of reagents that contain two sulfur atoms. For example, the achiral bis(phenylthio)methane becomes the chiral 1,3-dithiepine (eq 1), still maintaining similar structural features to the acyclic reagent.7 This dithiepine belongs to the class of reagents that function as formyl anion synthons. The C2 symmetry is also shared by the bisoxide (it forms stereoselectively as a single pseudoequatorial isomer) and the bis-sulfone. Reaction of the anion of the dithiepine with benzaldehyde gives an 8:2 mixture of diastereoisomers (eq 2).7

A single diastereoisomer is obtained in the reduction of the ketone with Lithium Aluminum Hydride as illustrated in eq 3.8 The addition of other nucleophiles such as methylmagnesium iodide also gives single adducts.

Monoxidation of the dithiepine gives single diastereomeric sulfoxides with pseudoequatorial configuration (eq 4).7 In general, the oxides exhibit increased diastereoselectivity with respect to the unoxidized substrates, as in the examples of eq 5.7

C2 symmetric, chiral ketene dithioacetals containing the binaphthyl moiety can be prepared by Peterson alkenation of the title reagent (eq 6).9 The corresponding bis-sulfone affords one exo and one endo adduct with cyclopentadiene (eq 7) which, once separated and desulfonylated, give the corresponding norbornenes (see 1,1-Bis(phenylsulfonyl)ethylene).10

The dithiocine tetraoxide derived from cyclocondensation of binaphthodithiol with dichloroethylene and oxidation (eq 8) is a chiral version of the bis(phenylsulfonyl)ethylenes.11 These compounds are useful acetylene equivalents in cycloaddition reactions (see 1,2-Bis(phenylsulfonyl)ethylene).9 Indeed, a chiral acetylene equivalent allows the preparation of optically active hydrocarbons which would be difficult to prepare by classical methods. The dithiocine tetroxide reacts with nonsymmetric dienes to give a single crystalline diastereomeric adduct in most cases. Adducts (1) and (2) were obtained from acyclic and cyclic dienes.

The addition provides only one stereoisomer out of the four possible ones. Sodium Amalgam reduction in buffered methanol removes the binaphthyl residue to afford the hydrocarbon and recovered starting dithiol.11

Finally, it is notable that the title reagent has been used to prepare even larger ring systems such as chiral crown ethers,3 and the use of 1,1-binaphthalene-2,2-dithiol as ligand for rhodium(I) in the asymmetric hydroformylation of styrene has been described.12

1. (a) De Lucchi, O. PS 1993, 74, 195. (b) Cossu, S.; De Lucchi, O.; Fabbri, D.; Licini, G.; Pasquato, L. OPP 1991, 23, 571. (c) Cossu, S.; De Lucchi, O.; Fabbri, D.; Fois M. P.; Maglioli, P. In Heteroatom Chemistry: ICHAC-2, Block, E., Ed.; VCH: New York, 1990; Chapter 8, pp 143-163.
2. (a) Barber, H. J.; Smiles, S. JCS 1928, 1141. (b) Armarego W. L. F.; Turner, E. E. JCS 1957, 13. (c) Murata, S.; Suzuki, T.; Yanagisawa, A.; Suga, S. JHC 1991, 28, 433.
3. Cram, D. M.; Helgeson, R. C.; Koga, K.; Kyba, E. P.; Madan, K.; Sousa, L. R.; Siegel, M. G.; Moreau, P.; Gokel, G. W.; Timko, J. M.; Sogah, G. D. Y. JOC 1978, 43, 2758.
4. Fabbri, D.; Delogu, G.; De Lucchi, O. JOC 1993, 58, 1748.
5. Cossu, S.; Delogu, G.; De Lucchi, O.; Fabbri, D.; Fois, M. P. SC 1989, 19, 3431.
6. Di Furia, F.; Licini, G.; Modena, G.; De Lucchi, O. TL 1989, 30, 2575.
7. (a) Delogu, G.; De Lucchi, O.; Licini, G. CC 1989, 411. (b) Delogu, G.; De Lucchi, O.; Maglioli, P.; Valle, G. JOC 1991, 56, 4467.
8. Delogu, G.; De Lucchi, O.; Maglioli, P. SL 1989, 28.
9. De Lucchi, O.; Fabbri, D.; Lucchini, V. SL 1991, 565.
10. De Lucchi, O.; Fabbri, D.; Lucchini, V. T 1992, 48, 1485.
11. (a) Cossu, S.; Delogu, G.; De Lucchi, O.; Fabbri, D.; Licini, G. AG(E) 1989, 28, 766. (b) De Lucchi, O.; Fabbri, D.; Cossu, S.; Valle, G. JOC 1991, 56, 1888. (c) Pindur, U.; Lutz, G.; Fischer, G.; Schollmeyer, D.; Massa, W.; Schröder, L. T 1993, 49, 2863.
12. Claver, C.; Castillon, S.; Ruiz, N.; Delogu, G.; Fabbri, D.; Gladiali, S. CC 1993, 1833.

Ottorino De Lucchi

Università di Venezia, Italy

Giulia Licini

Università di Padova, Italy

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