Jyn-elimination

The thermal jyn-elimination reactions of X-oxides have assumed great importance in synthesis because of their mildness and regioselectivity. 

The preference for jyn-elimination leading to the fra/ii-olefins is not too difficult to understand in the alicyclic series. The use of models clearly indicates that the non-reacting alkyl residue exerts a severe limitation on the 

This marked preference for 1,4-jyn-elimination is not surprising as it involves two simultaneous l,2-am/-eliminations. On the other hand, l,4-ant/-elimination involves a 1,2-an -elimination coupled with a 1,2-iy -c/ma/-elimination and consequently involves less favourable overlap of the developing p orbitals in the transition state. 

Realising the significance and necessity of jyn"-elimination in Ej processes. Barton showed that this concept correctly predicted the direction of elimination of xanthates and esters of many natural products, based on 5- and 6-membered alicyclic rings and he subsequently used this method to predict unknown configurations of certain compounds. 

In step 4, the elimination of HBr is reasonable because it gives an aromatic system and because jyn-E2 elimination is a common reaction. 

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