Noh nocoochhceocoocH

R7 R

rn^n© k2co3 rVNv

Scheme 4.15 Proposed mechanism for the synthesis of N-methyl oxazolinones from oximes.

reactions, respectively) in Scheme 4.15. This reaction is also the first ever reported example of a sigmatropic rearrangement involving DMC. We have gathered further evidence for this mechanism from the comparison of the reactivity of C5-C7 cyclic oximes, which is resumed in Scheme 4.16.

As can be seen, cyclohexanone- and cycloheptanone-oximes give the cyclic rearranged products, while cyclopentanone-oxime yields a complex reaction mixture with no traces of the corresponding oxazolinone. Since sigmatropic rearrangements proceed through a highly ordered transition state,36 the required geometry is perhaps not achieved when a more strained C=C bond is involved, as occurs in the rigid cyclopentene ring (Scheme 4.15). Also, the reaction of allylimines with DMC give rearranged products. As an example, N-cyclohexylideneallylimine undergoes N-methylation by DMC followed by an aza-Claisen rearrangement (Scheme 4.17).27

Scheme 4.16 The reactivity of C5-C7 cyclic oximes.

Was this article helpful?

0 0
Growing Soilless

Growing Soilless

This is an easy-to-follow, step-by-step guide to growing organic, healthy vegetable, herbs and house plants without soil. Clearly illustrated with black and white line drawings, the book covers every aspect of home hydroponic gardening.

Get My Free Ebook

Post a comment