Abstract

AbstractThe hetero‐Diels‐Alder addition of SO2 to (E)‐hexa‐1,3‐diene (4) gives first 6‐ethyl‐3,6‐dihydro‐1,2‐oxathiin 2‐oxide (= 6‐ethylsultine) with the Et group occupying a pseudoaxial position, and then the more stable stereoisomer 6 with the Et substituent in a pseudoequatorial position. The SO2 additions to 1‐methoxybuta‐1,3‐diene (7) and to 1‐methoxy‐3‐[(trimethylsilyl)oxy]buta‐1,3‐diene (8) give the 6‐methoxysultines 9 and 10, respectively, with the MeO groups in pseudoaxial positions and which do not equilibrate with sultines having pseudoequatorial MeO substituents (anomeric effect). A lower limit of ΔΔG = 3.9 kcal/mol was evaluated at −60° for the stabilizing effect arising from the geminal vicinity of a MeO and sulfinate moiety in 3,6‐dihydro‐6‐methoxy‐4‐[(trimethylsilyl)oxy]‐1,2‐oxathiin 2‐oxide.

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