endoExo - The terms endo and exo are used in two...

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The terms “endo” and “exo” are used in two distinctively different ways. (1) Stereochemical label for substituents on bridges, relative to other bridges. H Br OH H CH 3 H Bridged, bicyclic molecules have 3 bridges of atoms spanning the two bridgehead atoms: 1 atom bridge 3 atom bridge 2 atom bridge When a substituent on one bridge is cis to the larger of the other two bridges, the stereochemistry is call endo ; if it is cis to the smaller of the other two bridges, exo H Br OH H CH 3 H the “Br” is cis to the larger other bridge, so its stereochemistry is endo the “H” is cis to the smaller
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Unformatted text preview: of the other two bridges, so its stereochemistry is exo H Br OH H CH 3 H H Br OH H CH 3 H endo endo exo exo (2) When the EWG is the normal Diels-Alder reaction is tucked underneath the cavity formed by the diene, then this is called the endo transition state; if it is outside the cavity of the diene, then exo transition state EWG endo transition state allows for secondary orbital interaction if EWG has pi bonds EWG exo transition state H 3 CO H NO 2 H 3 C + O 2 N H H 3 CO H CH 3 H endo transition state NO 2 CH 3 H 3 CO H exo endo...
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