Groups 1,3-benzodithiol

The introduction of a 1,3-benzodithiol group in a stereoselective fashion can be used to generate an anionic or cationic equivalent and could be easy removed by Raney nickel. This procedure was applied to the synthesis arundic acid [34], which is currently undergoing phase 11 development for the treatment of acute ischemic stroke, and to the bisabolane skeleton (P. Canestrari, E. Emer, A. Gualandi, and P.G. Cozzi, unpubUshed results). The procedure was recently extended to the formation of quaternary stereogenic centers, in particular the alkylation of a-branched aldehydes with the benzodithiolyUum ion can be catalyzed by the use of 9-amino-9-deoxy-epi-dnchona alkaloid primary amines [35]. The use of primary... 

Very recently, Cozzi et al. successfully demonstrated the application of this methodology for the a-alkylation of the formyl group to enohzable aldehydes. This was achieved by a reaction of benzodithiolylium tetrafluoroborate (a stabilized carbenium ion) in the presence of several different substituted imidazolidin-4-ones [48]. After reductive removal of the benzodithiol group access to chiral a-branched primary alcohol is given. Using this method optically pure arundic acid is obtained by a three-step synthesis. 

A further example of the same type of rearrangement is afforded by the l 2-benzisothiazoline-3-thiones. If the benzisothiazolium salt (40) is treated with thioacetic acid, the product is the 3-arylimino-3/f-1,2-benzodithiole (41), provided R is an aryl group when R is alkyl, the product is the benzisothiazoline-3-thione (42).32 Structures of types 41 and 42 are, however, in equilibrium with each other at 150°, presumably via a dipolar intermediate [Eq. (3)].32 A diradical... 

Benzodithioles 285 (R1 = H) and 7,8-dimethyl-l,5-dihydro-2,4-benzodithiepins286 (R = H) have been used as precursors of formyl and acyl anion derivatives. The lithiation of compounds 285 takes place at —30 °C with n-BuLi and these anions are stable for long periods of time at this temperature454. They react with alkyl iodides, carbonyl compounds and epoxides, the addition to cyclohex-2-enone taking place at the carbonyl group. The deprotection has also been carried out with mercury(II) oxide and BF3 OEt2-... 

Other examples of functionalization at C-2 via phosphorus ylides and phosphonate carbanions are described in Section 4.12.11. Utilization of 2-non-phosphorus-containing carbanions was also exemplified. Thus, 2-silicon-substituted 1,3-benzodithioles were synthesized via deprotonation of benzo-l,3-dithiole 245 with -BuLi and subsequent treatment of the resulting anion with trimethylsilyl chloride (TMSCl) to give 2-(trimethylsilyl)-benzo-l,3-dithiole 246 (Scheme 29). The second silyl group was introduced by further deprotonation of 246 ( -BuLi) followed by the reaction with an additional equivalent of TMSCl. Tin-substituted benzo-l,3-dithioles were synthesized in a similar way but the deprotonation of the monostannyl derivative was carried out with LDA (Scheme 29) <1996CL171>. 

Ammonia and aromatic and aliphatic primary amines react similarly with a double molar amount of a 4,5-diphenyl-1,3-dithiolium or 1,3-benzodithiolium salt. Both amino hydrogens are replaceable by l,3-benzodithiol-2-yl groups, leading to compounds With secondary aliphatic... 

For conversions of l,3-benzodithiol-2-ium cations, substituted with electron-donating groups in position 2, into the corresponding 1,4,2-benzodithiazines, see the section above. 

Dithiobenzoates PhCS2R (R = allyl, propargyl, or benzyl) add to dimethyl acetylenedicarboxylate to form the dithioles (288) with migration of the group R. Piperidine catalyses the addition of acetylenic ketones Ar COC=CAr to 4-methylbenzene-l,2-dithiol to give the benzodithioles (289). The reaction of the acetal BrCH2CH(OEt)2 with ethanedithiol yields a mixture of the bis(dithiolan) (291) and derivatives of dithian, which are formed, respectively, from the cations (290) and (292). ... 

Solid 2-isopropyl-1,3-benzodithiole 1,1,3,3-tetroxide added to a suspension of NaH in THF, treated with 2-phenylethyl bromide when H2 evolution had ceased, and heated at 80° for 24h - intermediate (Y 75%), in methanol at 50° treated in 3 portions over 3 h with Mg-turnings, and worked up after ca. 4 h - 4-methylpentyl-benzene (Y 72%). This is part of a multistep synthesis of hydrocarbons from two halide molecules with insertion of a methylene group. F.e., also 1,1-disulfonylcyclo-pentanes from 1,4-diiodides, s. E.P. Kundig, A.F. Cunningham, Jr., Tetrahedron 44, 6855-60 (1988). 

Sulfurization of tricoordinated phosphorus compounds by treatment with 3H-1,2-benzodithiol-3-one 1,1-dioxide results from the nucleophilic attack of, for example, a phosphite triester on the electrophilic thiosulfonate function of 2 to produce the phos-phonium sulfinate intermediate 3 (eq 2). Intramolecular condensation of the sulfinate anion with the carbonyl group of the activated thiol ester function releases the phosphorothioate triester (4) with concomitant formation of 5. Because of the... 

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