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 Et 3 N 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 )/Et 3 N 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 )/Et 3 N and from mesyl chloride/Et 3 N, the [4 + 2] cycloadducts 6e and 6g were obtained. Similarly, methanedisulfonyl dichloride ( 1f , X = Cl)/Et 3 N afforded stereospecifically by two subsequent [4 + 2] cycloadditions the spirodisulfone 16 (X‐ray analysis).