Enamines rearrangement

Rearrangements of vinylogous urethanes to vinylogous carbonic acids and decarboxylation are other interesting enamine rearrangements which may be synthetically useful in the formation of cyclic enamines (623,624). 

An enamine rearrangement has been proposed for the formation of indole rings from pyridinium salt (51) (Scheme 35) <95IJC(B)(34)285>. 

Enamines obtained from secondary amines and 2-acylfurans undergo the acylfuran-enamine rearrangement with the formation of N-substituted o-aminophenols 297 (Scheme 11). 

Dipolar Additions (30) -Lactam Preparations (12) Ni-Coupling Reactions (3) Enamine Rearrangement (1)... 

Cyclopropanation products 59 of enamines rearrange to a-methyl or a-ethyl ketones 60 when heated in aqueous methanol in sealed tubes or when refluxed in aqueous methanol in the presence of 10% palladium on charcoal. ... 

Scheme 5.36. Involvement of the methoxymethyl in the asymmetric Michael addition (a) by dipolar stabilization of a zwitterion intermediate, or (b) by assisting in the proton transfer to the Michael acceptor, (c) Isolation of an addition product via enamine rearrangement [187].

Application of solid-state chemistry for quantitative multistep cascades in a ball mill is also demonstrated by reaction of enamine ketone 291 with 1,2-dibenzoylethene 292 (Scheme 3.78). Pyrrole derivative 293 was obtained by Kaupp et al. in quantitative yield through four reaction steps (vinylogous Michael addition, imine/enamine rearrangement, cyclization, and elimination), without the use of add catalysts [18]. 

A study of the preparation of ocimene by isomerization of a-pinene has been reported. a-Azidoacetophenones have been converted to 2-aryl-l,3-oxazole-4-carbaldehydes by rearrangement of the carbon framework on exposure to DMF/POCI3. The rearrangement occurs via alkenyl azides and 2//-azirines. Enamine rearrangement of pyridinium salts to indoles has been studied.Kinetic stabilization and reactivity of a series of singlet 2,2-dialkoxy-l,3-diphenyloctahydropentalene-l,3-diyls enable cis-selective formation of the ring-closed compounds (Scheme 105). ... 

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