Azines alkoxy, reactions

Reaction of 2,4,7-trichloroquinoline with sodium methoxide (65°, 30 min) yielded an equal mixture of 2,7-dichloro-4-methoxy- (40%) and 4,7-dichloro-2-methoxy-derivatives (31%). The activating effect of the chloro groups is evident from the inertness of 4-chloro-quinoUne to methoxide ion at 65°. Alteration of the relative reactivity by cationization of the azine ring is again noted here in the acid-catalyzed hydrolysis (dilute HCl, 100°, 1.5 hr) of the trichloro compound to give 72% of the 2-hydroxylation product.Similarly, acid-hydrolysis of the alkoxy group proceeds much more readily in 2-ethoxy-4-chloro- than in 4-ethoxy-2-chloro-quinoline. ... 

Only the E,3E stereoisomer of the 2-azadiene was found to be reactive under the reaction conditions. Consequently, each of the piperidine products was found to possess the cis 2-phenyl, 5-methyl relative stereochemistry. Moreover, the cycloaddition products derived from reactions of enol ethers possessed the all-cis 2-phenyl-4-alkoxy-5-methyl stereochemistry necessarily derived from exclusive endo cycloaddition. Dienophile geometry is maintained during the course of the [4 + 2] cycloaddition, and no products derived from a potential stepwise, addition-cyclization reaction were detected. Representative neutral and electron-deficient dienophiles failed to undergo cycloaddition. A related boron trifluoride etherate-catalyzed [4 + 2] cycloaddition of simple 2-aza-l,3-butadienes with carbonyl compounds provides 5,6-dihydro-2//-l,3-ox-azines and appears to proceed preferentially through an endo [4 + 2] transition state although evidence supporting a stepwise, addition-cycli-zation was occasionally detected.630... 

A novel fragmentation of iV-arylidene- or Al-(aLkylideneamino)- 8-lactams can be induced by ozone to lead to various enol ethers after a reductive workup with sodium borohydride. The starting 8-lactams can be prepared via [2 + 2] cycloaddition of alkoxy ketenes and an azine and upon treatment with ozone at low temperature, yield the expected secondary ozonides (eq 59). Reduction of the ozonide leads to the corresponding N-nitroso intermediate, which is susceptible to fragmentation of the C4—N1 bond to give a zwitterion intermediate that rearranges to yield the product enol ethers. In the reaction sequence, fra 5- 8-lactams yield predominantly the E-enol ether while the d5- 8-lactams preferentially form the Z-configured enol ethers. 

This feature of the reactions of azine W-oxides is of a general character. Indeed, the so-called deoxygenative nucleophilic transformations of azine W-oxides and their cationic forms into products have been established to involve the aMfo-aromatization step, in which the W-oxide, W-alkoxy, or W-acyloxy functions are auxiliary groups, facilitating elimination of hydrogen from the intermediate o -adducts (Scheme 19) [11, 45, 90-93] (for more details [215]). 

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