This thesis is divided into two major parts. The first part deals with the development of conditions for a Heck reaction to introduce aryl and vinyl substituents to the beta-position of crotonaldehyde and related alpha,beta-unsaturated aldehydes. The reaction provides very fast (<1 h) access to the desired beta,beta-disubstituted, alpha,beta-unsaturated aldehydes in typically good to very high yields. The methodology is furthermore employed in shortening the formerly lengthy synthesis of enantiopure Florhydral. The second and larger part concerns the development of the chemistry of N-Boc, N-Cbz, N Fmoc, and N-Bz-imines in proline-catalyzed Mannich reactions of unmodified aldehydes and ketones. The reactions are usually good to high in yield and with high to excellent levels of enantioselectivity. It also describes the first use of acetaldehyde as donor in an organocatalyzed reaction, leading to defined single-addition products of extremely high enantiopurity. Finally, the newly developed methodology was employed to synthesize the side chain of paclitaxel (taxol), and the semisynthesis thereof is presented
