............................................................................................................................................................. 5 Abbreviations ................................................................................................................................................. 7 Table of contents ........................................................................................................................................... 9 1 Aims of the thesis ................................................................................................................................... 13 2 Background ................................................................................................................................................. 15 2.1 Barettin ................................................................................................................................................. 15 2.2 Amino acids ........................................................................................................................................ 15 2.3 The Schöllkopf method .................................................................................................................. 16 2.3.1 Dipeptides ........................................................................................................................................ 17 2.3.2 Cyclization ....................................................................................................................................... 18 2.3.3 Diketopiperazine ........................................................................................................................... 18 2.3.4 Bis-O-alkylation and dealkylation .......................................................................................... 19 2.4 Importance of different bases ..................................................................................................... 20 2.5 Aldol addition or condensation................................................................................................... 21 2.6 Alkylation ............................................................................................................................................ 22 3 Results and Discussion ....................................................................................................................... 23 3.1 Synthesis of the dipeptide (5) ..................................................................................................... 23 3.2 Cyclization of the dipeptide (5) .................................................................................................. 23 3.2.1 Cyclization of 5 by conventional heating. ............................................................................ 23 3.2.2 Cyclization of 5 by microwave irradiation .......................................................................... 24 3.3 O-Ethylation of the 2,5-DKP (6) to form the bis-lactim ether (7) .................................. 25 3.4 Aldol condensation and alkylation reactions of (7) with different bases. ................. 26 3.4.1 Synthesis of aldol addition 9 and condensation 10 products with Cs2CO3 as the base. .............................................................................................................................................................. 27 3.4.2 Synthesis of aldol addition product 9 with k-tBuO/BuOH as the base. ................... 28 3.4.3 Synthesis of aldol addition product 9 with DBU as the base. ...................................... 28 3.4.4 Synthesis of aldol addition product 9 and aldol condensation product 10 with BuLi as the base. ....................................................................................................................................... 29 3.4.5 Synthesis of aldol addition product 9 and aldol condensation product 10 with LiHMDS as the base. ................................................................................................................................ 30 3.4.6 Synthesis of aldol addition product 9 with LDA as the base. ....................................... 30 3.4.7 Synthesis of aldol addition product 9 and aldol condensation product 10 with TMP as the base. ....................................................................................................................................... 30