1.3- Dithiols 1.2- dithiolanes

Dithiolane-fused oxadithiepins, widely used in the synthesis of charge-transfer complexes, are available by [3+4] substitution reactions of dithiolane dithiolates with di(chloromethyl) ether (see Section 13.16.9.4.1). 

C3S2 s s — — — l,2-Dithiolane-4-carboxylic acid 3-phenyl-l,2-dithiolylium iodide 4-methyl-1,2-dithiole-3-thione ... 

A carbonyl group can be protected as a sulfur derivative—for example, a dithio acetal or ketal, 1,3-dithiane, or 1,3-dithiolane—by reaction of the carbonyl compound in the presence of an acid catalyst with a thiol or dithiol. The derivatives are in general cleaved by reaction with Hg(II) salts or oxidation acidic hydrolysis is unsatisfactory. The acyclic derivatives are formed and hydrolyzed much more readily than their cyclic counterparts. Representative examples of formation and cleavage are shown below. 

Ethynylquinoxalme (144) and bis(isopropoxythiocarbonyl) disulfide (145) gave 2-(2-oxo-l,3-dithiol-3-yl)quinoxalme (146) [l,l -azo(cyclohexanecar-bonitrile), PhMe, reflux, N2, 7 h 77%] somewhat similarly, 2-(acetylethy-nyl)quinoxaline and 4-phenyl-l,3-dithiolane-2-thione gave 2-(5-acetyl-2-... 

In the synthesis of l,3-dithiolan-2-ones from spirocyclic intermediates, via episulfides, substituted tetrathiacyclododecane and the related pentathiacyclopentadecane were isolated in good yields <96JCS(P1)289>. Preparation and molecular dynamics studies of 2,5,8,17,20,23-hexathia[9.9]-p-cyclophane have been reported <96P4203>. The syntheses and properties of thiocrowned l,3-dithiole-2-thiones and their conversion to tetrathiafiilvenes via treatment with triethylphosphine have been described <96LA551>. 

The procedure for the preparation of a dithiolane from a hydroxy-methylene derivative of a ketone and ethylene dithiotosylate (ethane-1,2-dithiol di-p-toluenesulfonate) can be varied to produce dithianes when the latter reagent is replaced by trimethylene dithiotosylate.8,4 The dithiotosylates also react with enamine derivatives to produce dithiaspiro compounds.4,5... 

The preparation of dithianes from enamines by reaction with trimethylene dithiotosylate (propane-1,3-dithiol di-p-toluenesulfonate) has been applied with enamines derived from oholostan 3 one, aceto-acetic ester, and phenylacetone.6 7 Reactions of trimethylene dithiotosylate with hydroxymethylene derivatives of ketones also give rise to dithianes thus the hydroxymethylene derivative of cholest-4-en-3-one can be converted to 2,2-(trimethylenedithio)cholest-4-en-3-one. 1,3-Dithiolanes are obtained in a similar manner by reaction of ethylene dithiotosylate1 with the appropriately activated substrate.5,7... 

Reductive cleavage of 1,3-dithiolanes is accomplished in low yields with sodium in liquid ammonia and gives either dithiols or mercapto sulfides depending on substituents in position two [679]. 

Dithioketals, especially the cyclic dithiolanes and dithianes, are also useful carbonyl-protecting groups. These can be formed from the corresponding dithiols by Lewis acid-catalyzed reactions. The catalysts that are used include BF3, Mg(03SCF3)2, Zn(03SCF3)2, and LaCl3.100 S-Trimethylsilyl ethers of thiols and dithiols also react with ketones to form dithioketals.101... 

Di- -butylstannyl dithiolates also serve as sources of dithiolanes and dithianes. These reactions are catalyzed by di-u-butylstannyl triflate.102... 

New applications of dithioles and dithiolanes include evaluation of compounds such as 69 and 70 as flavour components <98MI177>, 71 for antimycotic activity <99MIP33826>, 72 for antiviral activity <99CC1245>, 73 for antifungal and antibacterial activity <99MI6> and use of 74 in prevention and heatment of asthma complications <99EUP909758>. 

New applications for 1,2-dithiole and dithiolane compounds include evaluation of dithiolanes such as 84 and 85 as flavour components <98MI177>, 86 as a new indigo chromophore <99T14429>, 87 as a fungicide and insecticide <99JAP11279179>, 88 as a... 

The stoichiometric equivalents of halofluorides have been recently applied to transform alkylene dithioacetals into gcm-difluorides.70-71 Dithioacetals such as 1,3-dithiolanes and 1,3-dithianes arc readily obtained from the corresponding carbonyl compounds by the reaction with ethane-1,2-dithiol or propane-1,3-dithiol in the presence of the complexes boron trifluoride-bis(acetic acid) or boron trifluoride-diethyl ether. Using a two-step procedure, a range of aldehydes and ketones can be converted into gem-difluorides under mild conditions. 

A general route to 1,2-dithiolanes (53) involves oxidation of the 1,3-dithiol (52) with hydrogen peroxide at 75°C in acetic acid containing potassium iodide. (3-Dithio compounds such as (54) undergo oxidation in acid to the 1,2-dithiolylium salts (55) (76JCS(D)455). 

The tobacco alkaloid nicotine (96) (B-67MI10702) is insecticidal by virtue of its action on the acetylcholine receptor. It was used widely as an aphicide, especially as a fumigant. Another natural product thought to act on the same receptor is the 1,2-dithiolane nereistoxin (97) (B-72MI10703), isolated from the marine annelid Lumbriconereis heteropoda. The active form has been shown to be the ring opened dithiol (98), and the protected form of it, cartap (99), is sold as a rice insecticide. The 1,2,3-trithiane thiocyclam (100) (72SAP7007824) is also active, presumably because of metabolic conversion to (98). 

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