Pyrido l,2-a azepines

The same group has developed another synthetically useful photochemically induced domino transformation. Irradiation of the enaminecarbaldehydes 5-40a or 5-40b in the presence of acrylic acid ester 5-41a or acrylonitrile 5-41b afforded the quinolizidines 5-45a and 5-45b as well as the pyrido[l,2-a]azepines 5-45c and 5-45d, respectively, with high stereoselectivity [14]. Only very small amounts of the corresponding diastereomers 5-46a-d were detected. 

The Chemistry of Pyrido[l,2-a] azepines and Their Hydro Derivatives... 

Finally Ebersbach s group succeeded in synthesizing the first (and, up to now, only known) authentic pyrido[l,2-a]azepine base 315 (Scheme 70) from their lactam 290 by thionation with Lawesson reagent (LR), methylation of thiolactam 313, and deprotonation of sulfenium salt 314 (91HCA1095). 

Irradiation of the alkynylenaminoester (145) (Scheme 23) in the presence of an alkene (R = C02Me, C02Bu , CN) yields the tetrahydropyridine (146) which undergoes acid-catalyzed cyclization to afford the pyrido[l,2-a]azepine (147) together with just a small amount of the Cioa epimer <92X2081 >. 

Figure 7.8 Alternative biosynthetic pathway for pyrido[l,2-a]azepine core.

Pyrido[l,2-a]azepines stemofoline. Stemona curtisii. NACE-MS 50 mM ammonium acetate, 1 M ESI-MS [77]... 

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