Cope rearrangement double diastereoselection

The next sequence relies on four mechanistic steps without any catalyst (Scheme 5.51) [134], First, a disubstituted vinyl-aziridine 145 adds to dimethyl-acetylenedicarboxylate to form a divinyl-aziridine 146, an appropriate substrate for an aza-Cope rearrangement. Delocalization of the double bonds of the resulting azepine is supposed to promote a disrotatory electrocyclization to the azabicyclo-[3.2.0]-heptane 147, which tautomerizes to the final product 148. The initial chirality of the aziridine and of the (Z)-configurated double bond control the full overall diastereoselectivity of the process thanks to the conservation of orbital symmetry. 

As shown by the rearrangement of 10, the second double bond of the pericyclic system can also be incorporated in a ring. Cope substrates 13. 16, 19. and 22 are obtained with high diastereoselectivity by addition of the corresponding cerium derivatives to 58 r)- 1063 "ftig dichlorocerium reagents proved to be superior to the vinyllithium reagents, as the latter cause excessive enolization. 

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