Thiophene dioxides synthesis

Benzo[6]thiophene, 3-aryl-2-methyl-1,1-dioxide synthesis, 4, 930... 

M. Passini, S. Destri, W. Porzio, C. Botta, and U. Giovanella, Electroluminescent poly(fluorene-co-thiophene-5,5-dioxide) synthesis, characterisation and structure-property relationships, J. Mater. Chem., 13 807-813, 2003. 

The primary adducts, cyclohexadiene derivatives, formed by [4+2] cycloaddition of thiophene dioxides with dienophiles, may further undergo [4+2] cycloaddition with the dienophiles. Thus, the adducts 84 of 3,4-di-ferf-butylthiophene dioxide 83 with maleic anhydride and AT-phenylmaleimide further react with these dienophiles to give excellent yields of bis-adducts, which are composed of the endo-endo and endo-exo isomers, 85a and 85b (Scheme 49) [160]. A similar reaction was also observed with 3,4-dichlorothiophene 1,1-dioxide with N-butyl- and A-p-nitrophenylmaleimides (Scheme 50) [133]. The reaction of highly congested thiophene dioxides 87 with 4-phenyl-1,2,4-triazoline-3,5-dione provides a unique pyridazine synthesis since the bis-adducts 88 are converted into the corresponding pyridazines 89 in one pot and in good yields by treatment with KOH in methanol (Scheme 51) [174]. 

The synthetically most important reaction that belongs to this category would be [4+2] cycloadditions of highly congested thiophene dioxides with alkynic dienophiles (Scheme 55) [39,40,159]. These reactions afford o-di-ferf-butyl-, o-dineopentyl-, and o-di(l-adamantyl)benzene derivatives in good yields, synthesis of which is very difficult by other means. 

The thiophene dioxide 166 (R = Me) photochemically adds to citraconic anhydride 168 to yield the adduct 169. This was subsequently used in a total synthesis of 10-hydroxygeraniol134. The parent sulpholene 167 (R = H) also undergoes (2 + 2)-photoaddition with dichloromaleimide to afford the adduct 170 (54%)135. 

The transmetallation of zirconium five-membered heterocycles by elemental selenium also affords selenophene derivatives with yields up to 50% <88JA2310>, Classical thermal displacement (210°C) of SO2 by selenium allowed the synthesis of 3,4-di-/-butylselenophene from the corresponding thiophene dioxide <90TL4473). 

Ethylene, /3-(dimethylamino)-nitro-in pyrrole synthesis, 4, 334 Ethylene, dithienyl-in photochromic processes, 1, 387 Ethylene, furyl-2-nitro-dipole moments, 4, 555 Ethylene, l-(3-indolyl)-2-(pyridyl)-photocyclization, 4, 285 Ethylene, l-(2-methyl-3-indolyl)-l,2-diphenyl-synthesis, 4, 232 Ethylene, (phenylthio)-photocyclization thiophenes from, 4, 880 Ethylene carbonate C NMR, 6, 754 microwave spectroscopy, 6, 751 photochemical chlorination, 6, 769 synthesis, 6, 780 Ethylene oxide as pharmaceutical, 1, 157 thiophene synthesis from, 4, 899 Ethylene sulfate — see 2,2-dioxide under 1,3,2-Dioxathiolane... 

Addition of amines to a,/J-unsaturated sulfones has been used in synthesis of key intermediates of biotin. In this reaction, benzylamine serves first as a base in the reaction with 60 to afford thiophene 1,1-dioxide (61) and also as a nucleophile to introduce two amino groups (equation 57)49. 

An interesting cycloheptatriene (182) synthesis has been described using thiophene 1, 1-dioxides (180) and cyclopropenes 181 (equation 121)ns. Concerted [4 + 2]cycloaddition and subsequent cheletropic extrusion of sulfur dioxide are suggested by the second-order kinetics (first in each reactant), and by the large negative activation entropy. 

During investigation of the synthesis of benzocyclobutane 193, Cava and coworkers118 found that o-quinodimethane 192, generated in the pyrolysis of 1,3-dihydrobenzo[c]thiophene 2,2-dioxide (191), can be trapped by Af-phenylmaleimide to give N-phenyl-1,2,3,4-tetrahydronaphthalene 2,3-dicarboimide (194) (equation 125). 

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