Synthesis of Azasteroids and Steroid Alkaloids

In a similar way to 1-oxa-l,3-butadienes, 2-aza-l,3-butadienes can also be prepared by condensation of an aldehyde such as 224 with anilines 225 to give, for example, novel azasteroids in a following cycloaddition reaction [60]. Thus, by condensa- 

160 5 The Domino-Knoevenagei-hetero-Dieis-Aider Reaction and Related Transformations 

As a side product in these reactions a novel bridged steroid alkaloid 230 is formed, presumable by an intermediate hydride shift in 227 from the benzylic position to the iminium ion to give a secondary amine, which then attacks the formed cationic benzylic position. This reaction becomes the main reaction with aniline, p-bromoaniline or nitroaniline in the presence of BF3 -OEt2 if a derivative of 224 is used containing a propyl instead of a propenyl side chain [61]. 

If R1 and/or R2 are hydrogen the selectivity drops nearly to zero. The transformation can also be performed in a two-step mode. Thus, imine 235 could be prepared by simple condensation of 233 and 234 in the presence of molecular sieves, and this then cyclized in the presence of SnCl4. 

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