Synthesis and some 4+3 cycloaddition chemistry of a sulfur-substituted allylic acetal

Abstract

The preparation of a sulfur-substituted allylic acetal is described and its application in 4+3 cycloaddition reactions with furan and cyclopentadiene is reported.

The (4+3)-cycloaddition reaction: heteroatom-substituted allylic cations as dienophiles

“…The results of this and our study are exciting. Most results fit the predictions made by theory, except for the stereostructure of 183 (eqn (31)). Is this structure correct?…”

“…of furan in CH 2 Cl 2 afforded the cycloadduct 61 in 70% yield (eqn (6)). 31 This process was not studied in detail and warrants further investigation. Trost showed that the reaction of allylic acetates such as 62 and 63 with palladium catalysts afforded stabilized trimethylenemethane intermediates capable of undergoing (4+3)-cycloaddition reactions with certain dienes (eqn ( 7)).…”

“…Before entertaining that last question, it should be noted that Walters published data concerning diastereoselective (4+3)-cycloadditions using his methodology. 75 For example, stirring 181 in the presence of furan and TEA in TFE afforded an 80% yield of cycloadduct 183 is a 95 : 5 ratio of diastereomers (eqn (31)). The result could be rationalized based on an endo approach of furan to the least hindered face of 182.…”

Catalytic Generation of Vinylthionium Ions. (4 + 3)-Cycloadditions and Friedel–Crafts Alkylations

“…In the context of our studies on (4 + 3)-cycloadditions, we introduced a number of methods for the generation of vinylthionium ions for use as dienophiles. These included the Pummerer rearrangement of allylic sulfoxides, the ionization of allylic sulfones, , the formation and concomitant ionization of selected allylic alcohols, and the ionization of certain allylic acetals as summarized in Scheme . We and others have used some of these methodologies in various applications …”