Desulfurization photochemical

A new synthetic route to alkyl-substituted quinones has relied on the photochemical reaction of 2,3-dichloro-l,4-naphthoquinone with a thiophene derivative (77CL851). Irradiation of a benzene solution of the quinone and thiophene by a high pressure mercury lamp gave photoadduct (295) in 56% yield. Desulfurization of this compound over Raney nickel (W-7) gave the 2-butyl-1,4-naphthoquinone derivative (296 Scheme 62). Alkyl-substituted quinones such as coenzyme Q and vitamin K, compounds of important biological activity, could possibly be prepared through such methodology. 

Aoyama et al. in relation to their studies on photochemical synthesis of (3-lactams [91] reported the synthesis of 4-spirocyclopropylazetidin-2-one [92] via photocycloaddition of 4-thioxoazetidin-2-one to alkenes followed by subsequent desulfurization. A solution of 1-isopropyl-3-phenyl-4-thioxoazetidin-2-one 70 and 1,1-diphenylethylene in benzene on irradiation with a high pressure mercury lamp afforded a [2 + 2] adduct 72 (R = Ph), in 67% yield which, on desulfurization with Raney-nickel [93] in anhydrous ethanol gave two isomeric... 

Photochemical desulfurization by irradiation of the sulfides in thiophilic solvents, e.g., trialkylphospites [10]. 

Besides photochemical desulfurization, sulfone pyrolysis allows for the broadest range of applications. The compounds which have been synthesized belong to classes as different as heterophanes, multilayered phanes, nonbenzenoid phanes, molecules containing molecular cavities or phenylenicen . The pyrolysis of sulfones in the gas phase in comparison with other methods has many advantages ... 

Besides their oxidation behaviour (Scheme 130) disulfides can be cleaved by hydrogen sulfide and may be desulfurized by photochemical means (80AHC(27)24l). With... 

Photochemically aided hydrogenolysis of allylic C-heteioatom bonds has anracted little interest. A few methods for debenzylation of ethers, amines and thiols, catalyzed by irradiation, have been utilized (see previous section also). An unusual desulfurization of benzyl thiol with triethyl phosphite (equation 94) in high yield, catalyzed by UV irradiation, is a useful alternative to other methods described in other parts of this chapter. 

Desulfurization of a number of thiols and disulfides, including the lipoic acid amide 174 under visible light irradiation, has received attention because of mild reaction conditions and the possibility to apply the same method in peptide chemistry (Scheme 23) <1999TA2643>. Accordingly, thioctic amide 174, that is, 5-(l,2-dithiolan-3-yl)pen-tanamide, was photochemically desulfurized in 36h in a one-pot reaction, giving 1-octanamide 175 in good yield. 

The first thiete fused to an aromatic system 219 (and an anthracene derivative) was reported in 1965 and was prepared by reduction of a naphthothiete sulfone. An attempt to prepare benzothiete by desulfurization of benzo-l,2-dithiolane was unsuccessful. Photolysis of benzo-l,2-dithiolane 1,1-dioxide in an attempt to extrude sulfur dioxide to give benzothiete also was unsuccessful. The naphthothiete 205, however, was prepared by extrusion of sulfur dioxide from 220 and nitrogen from 221. Thiete 205 also is obtained in 6-8% yield by treatment of 1,8-dehydronaphthalene with carbon disulfide. The unstable thiolactone 211 was formed by a photochemical extrusion of benzaldehyde from 222 and from 222a at 350°C. The benzothietes 209, 223, " and 224 have been... 

The photolysis of /rani-dibenzoylstilbene episulfide affords three primary products, trans- and cw-dibenzoyl stilbene (73 % and 16 % respectively) and cis-dibenzoyl stilbene episulfide . The cis episulfide gave essentially pure trans olefin. From exposure time studies it was concluded that the desulfurization of the trans episulfide is 97 % stereospecific and that most of the cis olefin originates from photoisomerization of the trans olefin. It was concluded that the initial photochemical... 

Photochemical desulfurization of thiocarbonates occurs with [Fe(CO)j] to give mononuclear as well as trinuclear (type 8) carbene complexes (24). A similar reaction affords desulfurization of diphenylcyclopropenethione (22). The thioketene cluster 13 reacts quantitatively, but in a more complicated way, with a thioketene to form a dinuclear vinylidene complex (14). 

The photochemical desulfurization of 4-amino-l,3 tWazolium salts 224 or mesoionic 2,3,5-triaryl-l,3-thiazolium-4-olates 228 in the presence of trialkylphosphite or trialkylphosphine, affording ring-opened cinnamic acid derivatives 226 [88JCS(P1)189] and 230 (83JHC245) or quinolinones 231 [88JCS(PI)189] is assumed to proceed via intermediate azetine derivatives 225 and 229, respectively (Scheme 62). 

---