Trapping reactions of sulfenes generated from sulfonic acid derivatives and bases, 1. Cyclopentadiene, methylcyclopentadiene and 1,2,3,4‐tetraphenylcyclopentadiene used as sulfene scavengers. [4 + 2] cycloaddition reactions and sulfonylations

The bulky sulfenes generated in situ from (+)‐10‐camphor‐, 10‐camphane‐, and 2‐methyl‐2‐phenylpropanesulfonyl chloride (1a–c) and Et3N can be trapped by cyclopentadiene to give the [4 + 2] cycloadducts 6a–c. The mixture of endo‐6a and exo‐6a (no other diastereomers) is formed by complete asymmetric induction. In MeCN solution additionally the 1,3‐di‐ and 1,2,4‐trisulfonylated cyclopentadienides 4a–c and 5a (X‐ray analysis) + 5c were obtained. On acidification, 4a and 5a were transformed into the pentafulvenoid derivatives 8a, 9a, 10a. The reaction of (+)‐10‐camphorsulfonyl chloride (1a)/Et3N with 1,2,3,4‐tetraphenylcyclopentadiene afforded the sulfonylated product 11a, with 2‐methylcyclopentadiene 50% endo‐12a (X‐ray analysis) and 10% exo‐12a. From cyclopentadiene and the more electrophilic cyanosulfene (2e) and mesylsulfene (2f, X = Me), generated in situ from cyanomethanesulfonyl chloride (1e)/Et3N and from mesyl chloride/Et3N, the [4 + 2] cycloadducts 6e and 6g were obtained. Similarly, methanedisulfonyl dichloride (1f, X = Cl)/Et3N afforded stereospecifically by two subsequent [4 + 2] cycloadditions the spirodisulfone 16 (X‐ray analysis).