Imine compounds electrocyclization reactions

Thus in the N-silyl substituted series, 17 and 18, which rearrange thermally to the corresponding diazo compounds, the stability increases through the series R=Me, Ph, i-Pr. As discussed below, these compound undergo the usual cycloaddition and electrocyclization reactions of nitrile imines and are not simply overstabilized curiosities. The usefulness in synthesis of those with P—C bonds is probably limited since these bonds are not easily broken, but products derived from those with C—Si and C—B bonds (e.g., 21 and 22) should be capable of further... 

Electrocyclization provides an efficient way to synthesize a large variety of heterocyclic compounds. Among the many photocyclization reactions of aromatic compounds, electrocyclization is among the most frequently studied. An example of this is that illustrated in Scheme 1. This involves cyclization between the arene moieties of the protonated azobenzene 1, which reacts from the jtJt state reaction and is controlled by the Woodward-Hoffmann rules. Six rr-electrons are involved in the conrotatory cyclization. The reaction was not observed when unprotonated azobenzene was irradiated because in this case, the ntt state is populated. Since the photochemical electrocyclization is reversible, a consecutive trapping reaction is needed to obtain the final products in good yields. In the present case, as in many other reactions, a rearomatization step via oxidation took place to afford the final product 2. In the same way, the imine 3 can be cyclized to the phenanthridine derivative 4. In this case, the oxidation of the... 

A new synthesis of ( )-crinan (43), a compound possessing the basic ring skeleton of the alkaloid crinine, using a stereoselective photocyclization reaction has been devised.28 The imine (39), readily prepared from 2-allylcyclohexanone and benzylamine, was acetylated with piperonyloyl chloride to give the AT-acylena-mine (40). Photolysis of (40) in methanol solution gave compound (41) (15% yield) whose structure and stereochemistry were established by spectral means and by consideration of the proposed electrocyclic nature of the reaction. 

The reaction of 3-imino-N,l,3-triphenylprop-l-enamine (14) with dimethyl acetylenedicarboxylate (DMAD) gives the pyridone (15). If the enamine is /8-disubstituted, as in compound (16), then initial attack occurs on the imine nitrogen rather than the enamine carbon. Electrocyclization followed by loss of aniline then yields the pyridine (17) (Scheme 8). ... 

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