2.5- Diketopiperazines, chiral, Diels-Alder reaction

Murray and colleagues199 developed some 2,5-diketopiperazines as new chiral auxiliaries and examined their asymmetric induction in the Diels-Alder reactions of their A-acryloyl derivatives with several dienes. Some of their results with dienophile 320 have been summarized in Table 19 (equation 89). When the benzyl group on 320 was substituted by an isopropyl or /-butyl group, the diastereofacial selectivity dropped dramatically. It was proposed that tv-tt stacking between the phenyl group and the electron-poor double bond provided a more selective shielding of one face of the double bond in this special case. 

Danishefsky s diene and imines to produce l,2-dialkyl-2,3-dihydro-4-pyridinones in high yields. Chiral non-racemic 2,5-diketopiperazine diene undergoes intermolecular hetero-Diels-Alder cycloaddition reactions with both c-rich and e-deficient alkene dienophiles, leading to bicyclo[2.2.2]diazaoctane structures. The regiochemical, stereoelectronic, and reactivity preferences of the diketopiperazine cycloadditions were investigated. ... 

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