Tetrahydrothiophenes catalysis

The synthesis of quinolizidine (3-spiro-2 )-tetrahydrothiophene (67a, 67b), a model compound for the synthesis of dimeric sulfur alkaloids, was reported (65, 66). The compound was prepared from 2-cyanotetrahydrothiophene (66) by two independent routes, both utilizing phase-transfer catalysis (Scheme 10). 

Aksenov D.G., Klimov O.V., Startsev A.N. (1997) Alumina supported sulfide catalysts. VI. Hydrogenolysis of tetrahydrothiophen. Kinet. Katal 38, 903-7. Yukelson 1.1., (1969) Methods of the Basic Organic Synthesis, Nauka, Moscow. Startsev A.N. (1995) The Mechanism of HDS Catalysis. Catai. Rev.-Sci. Eng., 37, 353-423. 

The addition of a diazocarbonyl compound to an alkene with metal catalysis is an effective method for the formation of cyclopropanes, as discussed above. However, direct addition to aldehydes, ketones or imines is normally poor. Epoxide or aziridine formation can be promoted by trapping the carbene with a sulfide to give an intermediate sulfur ylide, which then adds to the aldehyde or imine. For example, addition of tetrahydrothiophene to the rhodium carbenoid generated from phenyldiazomethane gave the ylide 131, which adds to benzaldehyde to give the trans epoxide 132 in high yield (4.104). On formation of the epoxide, the sulfide is released and hence the sulfide (and the rhodium complex) can be used in substoichiometric amounts. 

The ring exchange of tetrahydrofuran to tetrahydrothiophene is also catalyzed by basic sites and showed a decrease in activity with addition of HCl [8, 235]. However, pyridine adsorption also decreased the catalytic activity of the reaction on alkali-exchanged zeolites. In this case, acid and basic sites seem to be necessary for catalysis. 

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