Imine compounds exocyclic double bonds

On reduction, spireine afforded di- and tetrahydro derivatives. The location of two keto groups in spireine was revealed by H-NMR and mass spectral analysis of deuterated spireine and tetrahydrospireine. When spireine was heated with selenium at 340°, a compound with molecular formula C20H27NO2 was obtained. Structure 182 was proposed for this compound on the basis of spectral data. Since the C-19 imine bond is usually unstable and cannot be isolated in that form, we suggest that the imine bond is present at C-20 rather than at C-19 in the selenium degradation product (C2oH27N02). Thus, structure 183 should be considered for the latter. Each of the structures considered for spireine has unusual features. The exocyclic double bond in 181 bears some resemblance to lycoctamone (184), a rearrangement product of lycoctonine. 

The imines derived from 3-hydroxynaphtho[l,8-c]thiopyran-2-carbaldehyde and the corresponding 2-acetyl compound exist in solution in the keto-enamine 270, R1 = H, shown (Scheme 24). Irradiation at 436 nm results in reversible Z -E isomerization about the exocyclic double bond <1995ZOR1559>. 

NMR data have been recorded for numerous compounds with exocyclic enamine double bonds (79JHC1335). Examples of exocyclic imine double bonds are found in furan-2,3-dione 3-oxime and a related 5-oxime the vie proton coupling constant in the former is 5 Hz and so larger than expected, perhaps because of electron release from the hydroxy oxygen atom (72JCS(P1)2527). 

A variety of compounds may undergo cycloaddition at the C=C bond of vinylidenephosphoranes yielding exocyclic ylides. [2 -(- 2] Cycloadditions of Af-phenyliminovinylidenetriphenylphosphorane to electron poor double bonds of alkenes and imines lead to the formation of four-membered ylides (equation 112). ° ... 

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