α-Amino Acids and Derivatives in the Asymmetric Synthesis of Tetrahydroisoquinoline Alkaloids

Isoquinoline alkaloids are a small group of natural products with widespread occurrence in nature and also playing a very important role in the secondary metabolism of numerous vegetal families. In this context, during the last years the stereoselective synthesis of differently substituted tetrahydroisoquinolines has been a field of increasing interest in synthetic organic chemistry in which many research groups have focused much of their efforts. On the other hand, enantiopure α-amino acids and their derivatives have shown to be excellent tools for the organic chemist working in the field of asymmetric synthesis, either acting as chiral building blocks, auxiliaries or ligands. In this review, the different approaches for the asymmetric synthesis of substituted tetrahydroisoquinolines reported during the last years, in which chiral nonracemic α-amino acids or derivatives have played a crucial role will be presented. We have limited to the general procedures developed for the introduction of the desired substituents at the different positions of the tetrahydroisoquinoline core in a stereocontrolled way. However, some cases in which the obtained heterocycles have additionally been used as key synthetic intermediates for the easy preparation of other, naturally occurring, more elaborated, isoquinoline alkaloids have been covered.