A Sulfoxide-Based Ring Annelation Approach to Fused, Many-Membered Ring N,S-Heterocycles¹

Abstract

An approach to many-membered ring N,S-heterocycles involving sulfoxide electrophilic sulfenylation (SES) followed by ring expansion of the derived sulfonium salt intermediate (in situ) is illustrated for 9- and 10-membered-ring compounds. Treatment of readily prepared sulfoxides 10a, 10b, 18a, 18b, 23a, and 23b with triflic anhydride (pyridine, CH2Cl2, 0 °C) provides heterocycles 13a (65%), 13b (60%), 19a (67%), 19b (67%), 24a (42%), and 24b (80%), respectively. Sulfoxides 5a and 5b, under several different conditions, give only the Pummerer dehydration products 6a and 6b, respectively. Diastereomeric sulfoxides 18a‘ and 18b‘, upon treatment with triflic anhydride, do not produce clean product mixtures or any of the desired heterocyclic products but, upon heating in toluene, are converted to the more stable isomers 18a and 18b, respectively. Conducting this isomerization in the presence of 2-mercaptobenzothiazole produces a disulfide indicative of the intermediacy of a sulfenic acid. However, the importance of sulfenic acid derivatives in the SES process leading to many-membered ring heterocycles remains to be determined.

Observed and calculated 1H and 13C chemical shifts induced by the in situ oxidation of model sulfides to sulfoxides and sulfones

“…Compounds containing the sulfoxide and sulfone groups have been used as versatile intermediates in organic synthesis for carbon–carbon bond‐forming reactions,1–5 rearrangements6–8 and eliminations 9. They have also been used as catalysts for asymmetric synthesis 10.…”

1-[(1,3-Dihydro-2-benzothienyl)acetyl]-1H-indoleS-oxide

“…Crystals of the title compound (m.p. 471-474 K) were prepared as described previously (Bates & Xia, 1998) (7) ,~z, respectively. Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994).…”

“…The title compound, 1-[(1,3-dihydro-2-benzothienyl)acetyl]-lH-indole S-oxide, (I), was synthesized according to a method reported previously (Bates & Xia, 1998). The present study was conducted in order to verify the assignment of relative stereochemistry assessed by 1H NMR using aromatic solvent-induced shifts (Cooper et al, 1969), and IH-IH COSY (twodimensional correlated spectroscopy) and NOE (nuclear Overhauser effect) difference spectra (Bates & Xia, 1998). The original assignments did agree with the general chromatographic order of elution observed for diastereomeric sulfoxides (Portoghese & Telang, 1971).…”

Iron(III)‐Catalyzed Aerobic Oxidation and Cleavage/Formation of a C–S Bond

“…Compounds that contain a sulfone group have been widely used for a variety of reactions such as C–C bond formations,10 eliminations,11 and rearrangements12. Among the derivatives of sulfones, β‐oxo sulfones cannot only act as a versatile intermediates in Michael additions and Knoevenagel reactions13,14 but also work as valuable precursors in the preparation of ketones, chalcones,15 allenes, acetylenes, vinyl sulfones,16 and polyfunctionlized 4 H ‐pyrans 17.…”