Protecting-group-free synthesis

The introduction and removal of protecting groups are steps that unnecessarily increase the length of multistep syntheses. Hence, efficient syntheses are those that avoid the use of protecting groups. Protecting-group-free syntheses are highlighted in this review, in order to illustrate strategies by which the use of protecting groups can be minimized. 1 Introduction. 2 Early Examples 3 In the 21s' Century 3.1 Protection/Deprotection in situ 3.2 Biogenesis-Oriented Synthesis 3.3 Reliance on Transition-Metal-Catalysed Skeleton Formation 3.4 Order of Introduction of Functional Groups 4 Conclusion