1,4-Benzoxathians. 1. Reactions of o-mercaptophenol with .alpha.-halo Michael acceptors

Abstract

3-Ethylidino-2-oxo-1,4-benzodioxane (23). Reaction of catechol with 5b at 25°for 72 hr in the presence of KI gave 23 (18% yield): mp 74-75°(95% ethanol); nmr (CDCI3) 6.99 (s, 4, aro-

How Reaction Conditions May Influence the Regioselectivity in the Synthesis of 2,3-Dihydro-1,4-benzoxathiine Derivatives

“…To the best of our knowledge, the few existing synthetic procedures are dated, with harsh reaction conditions or troublesome work-up, and almost exclusively directed to 2-substituted derivatives (Scheme 1). [6][7][8][9][10][11][12][13] The first synthetic work 6 for the obtainment of this class of compounds concerns non-substituted 1,4-benzoxathianes (Scheme 1-A); Parham and coworkers used a strong-base catalysis, sodium methoxide, and yielded the desired and unstable products with only poor yields. This initial synthetic pathway was then fully overcome in the following years by one-pot procedures 7,8 (Scheme 1-B), in which suitably substituted cyclohexanones were treated with 1,2mercaptoethanol and a bromine source (NBS or CuBr2).…”

“…Further additional studies involved the treatment of 1,2-mercaptophenol with α-halo Michael acceptors 9 , methyl-4-bromobutenoate 10 or 2,3-dibromopropyl derivatives 11 , in acetone and using potassium carbonate as base (Scheme 1-C). In almost the totality of these works, the unique reaction products revealed to be the 2-substituted 1,4-benzoxathianes.…”

“…Literature showed the sole obtainment of 3-substituted 1,4-benzoxathianes only when β-methyl and β,β-dimethyl substituents were present in the α-halo Michael acceptors 9 (Scheme 1-D). Several alternative mechanisms were proposed in order to explain this opposite behavior; nevertheless, no reaction intermediates could be isolated to support those hypotheses.…”

“…To the best of our knowledge, the few existing synthetic procedures are dated, with harsh reaction conditions or troublesome workup, and almost exclusively directed to 2-substituted derivatives (Scheme ). − …”

Synthesis of Diospyrin, a Potential Agent Against Leishmaniasis and Related Parasitic Protozoan Diseases

“…For that purpose, 2-bromo-1-methoxy-3-methyl-1-trimethylsilyloxy-1,3-butadiene (8) was prepared from the known methyl 2-bromosenecioate (7). [22] A Diels-Alder reaction between 8 and 1,4-benzoquinone (9) proceeded in dichloromethane, and the resulting mixture was treated with dilute hydrochloric acid to remove the partly remaining trimethylsilyl group, giving a mixture of 10 and 11. This was fully methylated with methyl iodide and silver oxide to afford pure 11.…”