Retro aza Diels-Alder reactions in aqueous media

4 Retro aza Diels-Alder reactions in aqueous media 

The imino variant of the retro Diels-Alder process is known to require exceedingly high activation energies. Heterocycloreversion of 2-azanor-bomene has traditionally been conducted at temperatures in the range of 400-600 C in vacuo [33]  

These relatively mild conditions stand in sharp contrast to those employed in the first equation in this section. 

In the case of A -homoveratryl-2-azanorbonene, heterocycloreversion gives rise to a 61% yield of homoveratrylamine (103) along with 18% of the Pictet-Spengler cyclization product 102 derived from internal trapping of iminium ion 101  

More hindered AT-substituted 2-azanorbomenes smoothly undergo heterocycloreversion at room temperature. For example, exposure of a 0.84 M aqueous solution of the 2-azanorbomene derived from L-phenylalanyl-L-leucine methyl ester to 1.3equiv of A -methylmaleimide at ambient temperature gives rise to a nearly quantitative yield of the dipeptide ester with no detectable racemization  

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See also in sourсe #XX -- [ ]

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