[4 + 2] Cycloaddition of thiophene S-monoxides to activated methylenecyclopropanes

X-ray structural analyses and DFT study of 7-thianorbornenes: 4-aza-4-phenyl-10-thiatricyclo[5.2.1.0.2,6]deca-8-ene-3,5-dione and 4-aza-l,4,7-trimethyl-10-thiatricyclo[5.2.1.0.2,6]deca-8-ene-3,5-dione

“…The other way to increase the cycloaddition reactivity is by oxidation to thiophene-1-oxides and thiophene-1,1-dioxides, which are no longer aromatic [12][13][14][15]. Several structures of Diels-Alder adducts prepared in this way are reported in the literature and their X-ray structures are available for comparison [16][17][18][19][20].…”

High-Pressure Cycloaddition Reactions in the Synthesis of Biologically Relevant Heterocycles

“…The other methodology to increase the reactivity of thiophenes is reduction of aromaticity by oxidation of sulfur to thiophene S-oxide (Scheme 28) [46]. Reactions of thiophene S-oxides 115 with cyclopropenes 116 afforded under high-pressure 7-thiabicyclo[2.2.1]heptene S-oxides 117 in moderate-to-high yields.…”

Thiophene S-oxides

“…30 Already the generation of thiophene S-oxides by oxidation with peroxide and without isolation in the presence of dienophiles had shown their reactivity towards electron poor alkenes and alkynes (alkenes and alkynes with one or more electron withdrawing groups). 28 While the formal cycloadducts of thiophene S-oxides with alkynes, the 7-thiabicyclo[2.2.1]heptadiene S-oxides, extrude the sulfoxy bridge spontaneously and aromatise (22), the reaction of thiophene S-oxides with alkenes leads to 7-thiabicyclo[2.2.1]heptene S-oxides (20). 28 While the formal cycloadducts of thiophene S-oxides with alkynes, the 7-thiabicyclo[2.2.1]heptadiene S-oxides, extrude the sulfoxy bridge spontaneously and aromatise (22), the reaction of thiophene S-oxides with alkenes leads to 7-thiabicyclo[2.2.1]heptene S-oxides (20).…”

“…32 This stereochemical outcome has been observed for all of the cycloaddition reactions performed by the authors and has been ascertained by a number of X-ray crystal structural analyses by ourselves 8h,15,31e,32b and by other groups. 28 The thiophene S-oxide 2c can be reacted with N-[(ptoluenesulfonyl)imino]phenyliodinane (TsN=IPh) with [Cu(MeCN) 4 PF 6 ] as catalyst to form the thiophene sulfoximide 26 (Scheme 10). 31b,33 The activation barriers of both syn-and anti-addition have been calculated by semi-empirical methods 34,35 as well as at the RHF/6-31G* level.…”