Stereoselectivity three-membered ring formation

Stereoselectivity and Regioselectivity of Three-Membered Ring Formation from S Ylides... 

Good nucleophiles, such as ammonia and amines, open the highly strained epoxide ring by an S vj2 mechanism and show a regioselectivity for attack of the nucleophile at the less hindered carbon of the three-membered ring. The reaction favors the stereoselective formation of the trans product ... 

Purpose. Tbe third intermediate on the pathway to the target photochromic imine is synthesized. A heterocyclic three-membered ring, an aziridine derivative, is formed. This is the first ring of the diazabicyclohexene system that you will ultimately convert into the photochromic imine. You will study a process that involves three reactions and the formation of two intermediates en route to the final product. You will study a number of interesting stereoselective reactions. You wfll work with organic reactions that require several days to come to completion. 

A quinoxaline-related system can emerge upon the expansion not only of a five- but also a three-membered heterocycle. New frani-perhydroquinoxalin-2(lfl)-ones were prepared by the reaction of aziridines 449 with a-amino acids 312a, f as a result of the aziridine ring cleavage and pyrazine ring formation (Scheme 2.91) (Rees 1987). Note that the reaction is non-stereoselective and gives a mixture of products 450 and 451. 

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