Reaction with sulfur, selenium

E. Reactions with Sulfur, Selenium, tellurium. Phosphorus, AND Arsenic Derivatives... 

Ylides derived from imidazolium- and triazolium-substituted indole anions belong to the class of conjugated mesomeric betaines. Their tautomers are N-heterocyclic carbenes, which undergo trapping reactions with sulfur, selenium, and triethylborane, respectively. Deprotonation of the salts 45a—c with NaOH/EtOH produces the ylides 46a—c which are in tautomeric equihbrium with carbenes 47a—c (Scheme 36) (2014T8672). 

The Peterson reaction has two more advantages over the Wittig reaction 1. it is sometimes less vulnerable to sterical hindrance, and 2. groups, which are susceptible to nucleophilic substitution, are not attacked by silylated carbanions. The introduction of a methylene group into a sterically hindered ketone (R.K. Boeckman, Jr., 1973) and the syntheses of olefins with sulfur, selenium, silicon, or tin substituents (D. Seebach, 1973 B.T. Grdbel, 1974, 1977) illustrate useful applications. The reaction is, however, more limited and time consuming than the Wittig reaction, since metallated silicon derivatives are difficult to synthesize and their reactions are rarely stereoselective (T.H. Chan, 1974 ... 

Halogen fluorides react with sulfur, selenium, teUurium, phosphoms, sHicon, and boron at room temperature to form the corresponding fluorides. Slight warming may be needed to initiate the reactions (4) which, once started, proceed rapidly to completion accompanied by heat and light. The lack of protective film formation aHows complete reaction. 

So, this fact is strong evidence in favor of the intra- and inter-molecular dative P—B bond in 126. In solution, 126 is easily oxidized and undergoes addition reactions with sulfur and selenium, with the formation of the corresponding oxide (166), sulfide (167), or selenide (168) [Eq. (129)]. The 3,P chemical shifts of other compounds (166) (27 ppm), (167) (47 ppm), and (168) (46 ppm) are close to that observed for their structural analogues. These data and the values of dipole moments of 4,3 and 4,5 D for 166 and 167, respectively, make it possible to exclude the formation of intramolecular dative P—B bonds similar to those observed for borylphosphine ethene... 

Sulfur, at 345°C for thianthrene tetroxide, or at 250°C for thianthrene 5-oxide, produced thianthrene in good yields. S-Labeling experiments showed that the former took place with 80% replacement of ring sulfur and the latter took place with 91% replacement (73BCJ650), so these processes, whatever their detailed mechanism, do not involve simple reductive cleavage of the S—O bond. In accordance with this, thianthrene 5,5,10,10-tetroxide is converted into selenanthrene by reaction with elementary selenium (1896CB443). 

Reactions with sulfur and selenium in liquid ammonia yield hthium sulfide and selenide, respectively ... 

Our early work examined the reaction of PCTFE with sulfur, selenium and phosphorous nucleophiles 9 to achieve high levels of functionalization through a well-precedented (in the case of perfluoroalkyl iodides)20"24 one electron transfer, radical anion chain process. While such a reaction demonstrated the feasibility of using one-electron processes for the functionalization of PCTFE, the carbon-sulfur linkage remained susceptable to oxidation. 

Metallacyclopentadienes undergo a range of synthetically versatile reactions which proceed with extrusion of the metal atom and attendant ligands. Thus, reactions with alkenes and alkynes afford cyclohexa-1,3-dienes and arenes (Scheme 6), and thiophenes, selena-cyclopentadienes, pyrroles and cyclopentadienones (indenones, fluorenones) can be obtained by treatment with sulfur, selenium, nitroso compounds and CO, respectively. The best studied substrates for such reactions are cobaltacyclopentadienes of the type (24a), which have been converted into a wide variety of arenes, cyclohexadienes and five-membered heterocycles, many of which would be very difficult to obtain by conventional organic procedures (74TL4549, 77JOM(139)169, 80JCS(P2)1344). 

Reactions of organomagnesium compounds with sulfur, selenium and tellurium... 

Derivatives of phosphonic acids, RP==O(0H)2, can be prepared by several different oxidative methods. Primary phosphines RPH2 are oxidized to phosphonic acids by hydrogen peroxide or by sulfur dioxide thus, phenylphosphine gave benzenephosphonic acid (96%) on reaction with sulfur dioxide at room temperature in a sealed tube. Phosphinic acids, RI sO(OH)H, can also be oxidized to the corresponding phosphonic acids with hydrogen peroxide. Ozone oxidized the dioxaphosphorane (54) to the phosphonic ester in 73% yield. Ozone is also capable of stereospecific oxidation of phosphite esters to phosphates. For example, the cyclic phosphite (SS) was oxidized to the phosphate (56) with retention of configuration. Peroxy acids and selenium dioxide are other common oxidants for phosphite esters. 

Selenium, Se (its red modification), has been successfully employed for dehydrogenations of six-membered rings to aromatic systems. Compared with sulfur, selenium requires higher temperatures. Consequently, side reactions such as rearrangements occur [493]. 

The reactions with sulfur or selenium result in the formation of betaines, which can be alkylated to give semi-ylide salts (equation 98). The reactions of hexaphenylcarbodiphosphorane with a series of heteroallenes also lead to betaines which on thermolysis yield new cumulated ylides (equation 99, cf. equation 120). 

---