Henry J. Shine

Reaction of thianthrene cation radical with alcohols: Cyclohexanols

Abstract Cyclohexanol ( 1 ), 4-methylcyclohexanol ( 2 ), 4- tert -butylcyclohexanol ( 3 ), cis -2-methyl- ( 4 ) and trans -2-methylcyclohexanol ( 5 ) reacted cleanly with thianthrene cation radical perchlorate (Th .+ ClO 4 − ) in the presence of 2,6-di- tert -butyl-4-methylpyridine (DTBMP). The alcohols were converted quantitatively into cyclohexenes, while Th .+ was converted quantitatively into thianthrene (Th) and thianthrene 5-oxide (ThO). The oxygen atom of ThO came from the alcohol, as was demonstrated with the use of [ 18 O]cyclohexanol.

Reaction of thianthrene cation radical with grignard reagents : Evidence for electron transfer and trapping of alkyl radicals by the thianthrene cation radical

Abstract Reactions are reported between RMgCl and thianthrene cation radical perchlorate (Th .+ ClO - 4 ) suspended in ether and tetrahydrofuran (THF). In ether solution reactions R = Bu, s-Bu, t-Bu, 5-hexenyl, and cyclopentylmethyl. Major products were the alkane, the alkene R(-H) in some cases, and, in the cases of R = Bu, 5-hexenyl, and cyclopentylmethyl, the 5-alkylthianthrenium perchlorate (ThR + ClO - 4 ). When 5-hexenylMgCl was used a mixture of 5-(5-hexenyl)- and 5-(cyclopentylmethyl)thianthrenium per-chlorates in the ratio of approximately 2 was obtained. Since the ratio of 5-hexenyl/cyclopentylmethyl in the Grignard reagent was 10.4, it is concluded that the C 6 sulfonium ions were formed by radical trapping by Th .+ after single electron transfer from Grignard to cation radical had occurred, thus allowing for cyclization of 5-hexenyl radical. Formation of ThBu + ClO - 4 is attributed to the trapping of butyl radical by Th ·+ , while formation of RH and R(-H) is in all cases also attributed to alkyl radical reactions. Reactions in THF(R = Me, i-Pr, Bu, s-Bu, t-Bu, Ph) led almost exclusively to RH and Th. Polymerization of THF was also initiated and took place slowly giving rise to low molecular weight poly(THF). By using THF- d 8 , as solvent for reaction between BuMgCl and Th .+ , it was possible to find Bu groups ( 1 H-NMR) in the poly(THF- d 8 ). Polymerization of THF is attributed, in some cases (R = Me, Bu), to alkyl-cation transfer from ThR + to THF. In other cases initiation of polymerization by R + and THF(-H) + is considered.

1,3-dipolar cycloadditions induced by cation radicals. Formation of 1,2,4-triazoles from oxidative addition of 1,4-diphenylazomethane and aryl aldehyde phenylhydrazones to nitriles

Abstract Reaction of thianthrene cation radical perchlorate (Th.+ClO4−) with 1,4-diphenylazomethane (DPAM) in MeCN and EtCN led to the formation of 1,2,4-triazoles. Triazoles formation is attributed to oxidative cycloaddition of benzaldehyde benzylhydrazone, the tautomer of DPAM, to the solvent nitriles. In confirmation, analogous cycloadditions were achieved by reaction of Th.+ClO4− with some benzaldehyde phenylhydrazones in the same solvents.

Reactions of 5‐(alkyl)thianthrenium and other sulfonium salts with nucleophiles

A series of 5-(alkyl)thianthrenium triflates (3a–d, g–i) with alkyl (R) groups Me (a), Et (b), isoPr (c), 2-Bu (d), cyclopentyl (g), cyclohexyl (h) and cycloheptyl (i) were prepared by alkylation of thianthrene (Th) with alkyl formate and trifluoromethanesulfonic (triflic) acid. Benzylation (3f) was achieved with benzyl bromide and silver triflate. 5-(Neopentyl)thianthrenium perchlorate (3e) was prepared by reaction of thianthrene cation radical perchlorate with dineopentyl mercury. Methyl- (4a) and cyclohexyldiphenylsulfonium triflate (4b) were made by alkylation of diphenyl sulfide. Benzyldimethyl- (5a), dibenzylmethyl- (5b) and benzylmethylphenylsulfonium perchlorate (5c) were prepared in standard ways. Reactions of these sulfonium salts with iodide ion and thiophenoxide ion were studied for comparison with our earlier reported reactions of comparable 5-(alkoxy)thianthrenium and methoxydiphenylsulfonium salts. It is deduced that reactions of 3–5 with nucleophiles (Nu−) I− and PhS− follow traditional SN2 and E2C paths. Thus, the salts 3a–c, e and f gave virtually quantitative yields of RNu and Th, while small amounts of butene(s) were obtained from 3d. The cycloalkyl salts 3g–i gave amounts of cycloalkylNu and cycloalkene typical of competition of SN2 and E2C routes in the classical reactions of cycloalkyl halides and tosylates with I− and PhS− ions. Whereas 4a gave only SN2 products, 4b gave SN2 and E2C products typical of SN2/E2C competition. Among the salts 5a–c displacement of the benzyl group was dominant (5a) or exclusive (5b, c), thus exhibiting the preferential displacement of a benzyl group that has been fully documented in earlier studies of SN2 reactions. Qualitative comparison showed that 3a (methyl) reacted much faster than 3e (neopentyl) with PhS−. Unlike alkoxysulfonium salts, the salts 3–5 do not appear to undergo reactions at the sulfonium sulfur atom. Copyright

Reaction of thianthrene cation radical with alcohols: Isolation and chemistry of 5-cyclohexyloxythianthreniumyl perchlorate

Abstract 5-Cyclohexyloxythianthreniumyl perchlorate ( 1 ) was prepared by reaction of thianthrene cation radical perchlorate (Th •+ ClO 4 − ) with cyclohexanol in CH 2 Cl 2 . Cyclohexene and thianthrene 5-oxide (ThO) are formed when 1 is heated in solution. Reaction of 1 with H 2 O OH − occurs at the 5-position and gives cyclohexanol and ThO. The chemistry of isolated 1 clarifies earlier work on the reaction of Th •+ ClO 4 − with cyclohexanol.

An overview of some reactions of thianthrene cation radical. Products and mechanisms of their formation

A comprehensive review of recent chemistry of thianthrene cation radical is presented. Particularly, products and mechanisms of their formation from reactions with azo compounds, hydrazones, oximes, sulfonamides, alcohols, phenols, alkenes, alkynes and organometallics are discussed. Also, reactions of 5-(substituted)thianthrenium salts are reviewed.

Reactions of nucleophiles with 5-(alkoxy)thianthrenium ions

Reactions of 5-(alkoxy)thianthrenium perchlorates (1) with weakly basic nucleophiles Br−, I− and PhS− (X−) in MeCN and DMSO led to SN2 substitution, E2C elimination, and reaction at sulfonium sulfur to extents depending on the structure of the alkoxy group (RO) in 1 and the nucleophile. Three types of reaction occurred with R = cyclopentyl (1a), cyclohexyl (1b), cis- (1c) and trans- 4-methylcyclohexyl (1d) and cycloheptyl (1e), and X− = Br− and I−. That is, SN2 reaction gave RX and thianthrene 5-oxide (ThO), E2C reaction gave cycloalkene and ThO and reaction at sulfonium sulfur gave X2, thianthrene (Th) and cycloalkanol (ROH). Earlier work with R = Me (1f) and Et (1g) and X− = I−, Br− had shown that only SN2 reaction occurred. In contrast with reactions of halide ions, reactions of PhS− with 1b–g occurred only at sulfonium sulfur, giving Th, ROH and PhSSPh (DPDS). For comparison with 1, reactions of Ph2S+OMe (2) with I− and PhS− were carried out. Reaction with I− gave only Ph2SO and MeI (SN2). Reaction with PhS− gave very little PhSMe (SN2) but mainly Ph2S, MeOH, and DPDS from reaction at sulfonium sulfur. The differences in nucleophilic pathways (PhS− vs Br− and I−) in reactions with 1 and 2 are attributed to differences in thiophilicities of the nucleophiles. The thiophilicity of PhS− dominates its reactions with 1 and 2. The direction toward products (Th, ROH and DPDS) in these reactions is compounded by the ease of displacement of alkoxide from 1 and 2 by PhS−, and the ease with which, subsequently, thiophilic PhS− attacks sulfenyl sulfur in the resulting phenylthiosulfonium ion. Copyright

Electron-Transfer Reactions of Organosulfur Cation Radicals

Abstract The thianthrene cation radical (Th˙+) undergoes electron transfer in reactions with a number of azoalkanes. The oxidized azoalkanes then enter primarily into carbocation reaction pathways rather than the free radical pathways with which they are commonly associated. Examples are given with 1,1′-azoadamantane, phenylazotriphenylmethane, azotoluene, and azo-tertiary-butane. Reactions of Th˙+ with Grignard agents also result, to varying extents, in electron transfer from the Grignard to Th˙+. Here again carbocation chemistry is seen but particularly with solvent tetrahydrofuran, which polymerizes. The Grignard group may end up primarily as alkane (e.g., with t-butyl) or may also be trapped by Th˙+ in the form of a 5-alkylthianthre-niumyl ion (e.g. with butyl). Possible mechanisms of reactions are discussed

The nitramine rearrangement: support of nonconcertedness from heavy-atom kinetic isotope effects

On mesure les effets isotopiques cinetiques des atomes lourds ( 14 C et 15 N) dans la formation de nitro-2-, et nitro-4 N-methyl anilines au cours de la transposition, catalysee par les acides, de la N-nitro N-methyl aniline

Reactions of thianthrene cation radical with acyclic α, ω-diols: Formation of monoadducts and bisadducts. Intramolecular cyclization of monoadducts to cyclic ethers

Reactions of thianthrene cation radical tetrafluoroborate ( ) with α, ω-diols, HO(CH2) n OH (4b–g, n=5, 6, 8–10, 12), at the molar ratio Th•+:4 2/1 in MeCN containing 2,6-di-tert-butyl-4-methylpyridine (DTBMP) led to formation of bisadducts, α, ω-di(5-thianthreniumoxy)alkane ditetrafluoroborates (7b–g). Reactions with 4b,c gave also the cyclic ethers 6b,c by intramolecular cyclization. Preparation of the bisadduct (7a) from 1,4-butanediol (4a) was achieved only in the absence of DTBMP, in low yield. The major product was tetrahydrofuran (THF, 6a). Reactions of with 4b–g in the molar ratio 1/6, carried out in MeCN without DTBMP, led to the formation of monoadducts, α-hydroxy-ω-(5-thianthreniumoxy)alkane tetrafluoroborates (5b–g). Reactions with 4b,c led again also to cyclic ethers 6b,c. Cyclization of adducts to ethers (6b,c) was confirmed with the isolated monoadducts (5b,c). Attempts to prepare a monoadduct (5a) from 4a were unsuccessful; only THF (6a) was obtained. 5b–g and 7a–g were characterized with 1H and 13C NMR spectroscopy. Reactions of 7b,c with basic alumina resulted in formation of 4b,c rather than in elimination of thianthrene oxide and formation of linear dienes.