Cycloaddition reactions of the anhydro-4-hydroxythiazolium hydroxide system with dimethyl maleate and dimethyl fumarate

Synthesis of Dihydrothiophenes by an Amino-Directed Thioisomünchnone−Alkene Cycloaddition Reaction

“…At first sight, four possible approaches of the reactants may be envisaged for the cycloaddition process ( exo ‐up, exo ‐down, endo ‐up, and endo ‐down). Previous work10b and the steric hindrance caused by the bulky chiral fragment fused to the mesoionic heterocycle would suggest a preferential exo ‐up orientation. Scheme depicts both exo ‐up and exo ‐down approaches of maleic anhydride toward the mesoionic heterocycle.…”

“…However, the successful experiment with methyl vinyl ketone reveals that this dissociative pathway, which relies on the acidity of this α‐hydrogen atom, is unlikely to be a prime factor controlling the reaction outcome since this proton would not be sufficiently acidic in the corresponding oxo adduct. Moreover, early studies demonstrated that 2‐aryl‐substituted thioisomünchnones react with dimethyl maleate and dimethyl fumarate to preferentially afford exo cycloadducts, which do not undergo further fragmentation despite the acidity of the aforementioned hydrogen atom 10b…”

Desulphuration of sulphur bridged hexahydrotriazines: ring contraction to imidazolidines

“…Light petroleum refers to the fraction with a boiling range of 40-60 "C. E. Merck silica gel 60 (70-230 mesh) was used for chromatography. Raney 630 4(3) 0.771 4(3) 0.815 l(5) 0.646 7(4) 0.570 O(4) 0.619 3(4) 0.7 15 5(4 431 6(3) 0.057 4(3) 0.151 8(4) 0.062 7(4) 0.167 5(4) 0.277 9(4 383 2(4) 0.195 9(4) 0.151 9(5) 0.221 l(4) 0.230 l(4) 0.216 9(4) 0.1 10 6(5) 0.236 O( 5) 0.136 O( 5) 0.176 6( 7) 0.311 3( 7) 0.407 7( 6) 0.368 7( 5) 0.234 l (5) Estimated standard deviations in the least significant digits are shown in parentheses. X 0.606 6(4) 0.577 3( 5) 0.555 4(5) 0.560 4(6) 0.587 O (5) 0.…”

“…Raney 630 4(3) 0.771 4(3) 0.815 l(5) 0.646 7(4) 0.570 O(4) 0.619 3(4) 0.7 15 5(4 431 6(3) 0.057 4(3) 0.151 8(4) 0.062 7(4) 0.167 5(4) 0.277 9(4 383 2(4) 0.195 9(4) 0.151 9(5) 0.221 l(4) 0.230 l(4) 0.216 9(4) 0.1 10 6(5) 0.236 O( 5) 0.136 O( 5) 0.176 6( 7) 0.311 3( 7) 0.407 7( 6) 0.368 7( 5) 0.234 l (5) Estimated standard deviations in the least significant digits are shown in parentheses. X 0.606 6(4) 0.577 3( 5) 0.555 4(5) 0.560 4(6) 0.587 O (5) 0. 437 5(4) 0.255 2(4) 0.222 5(5) 0.673 5(5) 0.676 6( 5 ) 0.790 2(5) 0.760 5(4) 0.710 5( 5…”

Asymmetric [4 + 2] annulation of 5H-thiazol-4-ones with a chiral dipeptide-based Brønsted base catalyst

“…1g – j , 3 As an alternative, in 1975, Foucaud and co-workers described an example using 4-hydroxy-1,3-thiazoles as dienes to undergo [4 + 2] annulation with dimethylmaleate and dimethylfumarate. 4 Unfortunately, to date, no asymmetric method has yet been developed to access these entities in a non-racemic form.…”