2-Pyridyldimethylsilyl as a Removable Hydrophilic Group in Aqueous Diels-Alder Reactions This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports, and Culture, Japan, and in part by the Mitsubishi Foundation. We thank Professor Kazunari Akiyoshi (Kyoto University) for assistance with dynamic light-scattering experiments and fruitful discussions. Professor Susumu Yoshikawa and Professor Masahiro Kinoshita (Kyoto University) are gratefully acknowledged for critical discussions.