Y- Dithiolactones

Allenylsilver(I) compounds are prepared in situ by deprotonation of the allenic hydrocarbon with n-butyllithium and subsequent treatment with silver bromide (equation 5).19 Allenylsilver compounds afford allenic derivatives when treated with a variety of electrophiles, without significant isomerization to the propargyl system (equation 6).19,20 Reaction of the allenylsilver compound with carbon disulfide results in an interesting transformation to p,y-unsaturated-y-dithiolactones presumably by way of silver salts (Scheme ll).19,21... 

The synthesis of the five-membered cyclic dithioate 65 is shown in Scheme 16 [52,53]. The parent y-dithiolactone (3,4,5-trihydrothiophene-2-thione) (146) is prepared by thionation of the corresponding thiolactone 147, as shown in Eq. 32 [74]. Preparations for the l,3-dithiolane-4-thione derivatives 148 have been reported [75,76] (Scheme 32). It was proposed that the adamantanespiro compound 148a was formed by a reaction of the thiocarbonyl ylide, generated from 149 by extrusion of N2, with carbon disulfide [75]. 

Several approaches to cyclic thio- and dithio-lactones have been described thus, the reaction of y-oxo-esters with HjS gave 5-mercaptothiolan-2-ones (123) (see Vol. 5, p. 249). A general approach to y- and -thiolactones, e.g. (124), involves the reaction of a bis-metallated thioacid with a- or /6-chloro-ketones and cyclization of the resulting y- or <5-chloro-y6-hydroxy-thioacids. Reactions of cyclic lactones with the dimeric phenylthionophosphine sulphide (125) gave dithiolactones. y-Dithiolactones, e.g. (126), were obtained from 2-alkenyl alkanedithioates, which... 

A convenient preparation of /3,y-unsaturated-y-dithiolactones (205) has also been developed, from the reaction of allenyl-silver(l) compounds (204) with carbon disulphide. Cyclization of the initially formed adducts again occurs spontaneously to provide reasonable yields of these useful compounds. 

This 1,3-migration of hydrogen was also observed when 40 reacted with Lawesson s reagent to produce the dithiolactone 41. However, when y-hydroxy-a,P-unsaturated aldehyde 42 was reacted under similar conditions, thiophene 43 was prepared efficiently. These results are not surprising considering that the oxidation state of 42 is equivalent to the traditional saturated 1,4-dicarbonyl substrates of the Paal thiophene reaction via tautomerization of the double bond, and aromaticity is reestablished in the fully conjugated 43. 

A spirocyclic dithiolactone 65 was synthesized in high yield by sulfenyl group-assisted dehydration followed by intramolecular cyclization of P-hydroxy y-(phenylthio) dithioate66 (Scheme 16) [52,53]. 

The reaction is completed within 5-15 min if tetralin at 210 °C is used as solvent. Also, dithio-y-lactones, including dithio-phthalides and dithio-Q -p)Tones, are formed smoothly whereas the hitherto unknown simple or 3-dithiolactones cannot be prepared, neither with LR nor by any other method. Interestingly, dithiopilocarpine is formed as a mixture of diastereomers on reaction of pilocarpine with LR (eq 16), i.e. both oxygen atoms of (12) are replaced by sulfur. In an interesting sequence of thion-ation and rearrangement reactions, three different thiono analogs of 1,8-naphthalic anhydride were prepared (eq 17). ... 

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