The previous post showed how the 2+2 cycloaddition of an alkene could occur by a sort of sideways insinuation of the bonds. I have also shown how the same reaction can occur with a dramatic rotation of one of the double bonds. This post compares the two moves side by side.
| 0.0 | 5.3 kcal/mol |
 The forbidden dance |
 The allowed dance. |
As is sometimes the case in real life, the forbidden option has the lower activation barrier!
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Tags: pericyclic, Tutorial material