The main protecting groups for nitrogen used in the synthesis of peptides are the Boc, Cbz (Z), FMOC and Trityl groups. Discuss the use of these protecting groups in peptide synthesis, including showing the conditions used for their introduction and removal.

Aromatisation and re-aromatisation are important driving forces in the synthesis of compounds containing, and also for synthesising, aromatic heterocycles. Discuss this statement, using appropriate examples to help to illustrate your answer.        

Describe the use of acyl anion equivalents in synthesis. Use appropriate chemical structures to illustrate your answer.

"The Diels-Alder reaction is one of the most powerful reactions in Organic Synthesis". Discuss this statement, using appropriate examples to illustrate you answer.