Vinylogous relationships

Only very few papers report the oxidation of 4-substituted pyridinium salts (58CPB615 59JOC196 70JPC2027). Substituents in positions 2 and 4 might be expected to react similarly due to their vinylogous relationship to each other. This was, however, not confirmed for most of the numerous compounds studied (82UP1). 

FIGURE 14.28 The vinylogous relationship between the carbonyl and the amino group in pyrroline-3-ones gives them the reactivity of secondary amidesd ... 

Having retraced the remarkably efficient sequences of reactions which led to syntheses of key intermediates 14 and 15, we are now in a position to address their union and the completion of the synthesis of the spiroketal subunit (Scheme 6b). Regiocontrolled deprotonation of hydrazone 14 with lithium diisopropylamide (LDA), prepared from diisopropylamine and halide-free methyl-lithium in ether, furnishes a metalloenamine which undergoes smooth acylation when treated with A-methoxy-A-methylcarboxa-mide 15 to give the desired vinylogous amide 13 in 90% yield. It is instructive to take note of the spatial relationship between the... 

Attempts to liberate l-methyl-l-aza-2,3-cyclohexadiene (329) from 3-bromo-l-methyl-l,2,5,6-tetrahydropyridine (326) by KOtBu in the presence of [18]crown-6 and furan or styrene did not lead to products that could have been ascribed to the intermediacy of 329 (Scheme 6.70) [156], Even if there is no doubt as to the allene nature of 329 on the basis of the calculations on the isopyridine 179 and 3d2-lH-quinoline (257), it is conceivable that the zwitterion 329-Za is only a few kcal mol-1 less stable than 329. This relationship could foster the reactivity of 329 towards the tert-butoxide ion to an extent that cycloadditions to activated alkenes would be too slow to compete. On the other hand, the ultimate product of the trapping of 329 by KOtBu could have been an N,0-acetal or a vinylogous N,0-acetal, which might not have survived the workup (see, for example, the sensitivity of the N,0-acetal 262 [14], Scheme 6.57). 

The herbicidal activity of sulfonylureas derived from phenylacetic esters is enhanced when the carboxylate moiety is tied up to form a butyrolactone ring. Extension of this structural modification to weakly herbicidal sulfonylureas derived from cinnamate esters gives vinylogous butyrolactones which display significantly improved efficacy. Structure-activity relationships in these two classes of compounds are discussed along with their synthesis involving a novel benzothiazinone dianion and rf/h9-metallation chemistry. 

Solvolysis kinetics of allyl bromide in several alcohols have been studied. Kinetics of the reaction of methyl iodide with a solvatochromic vinylogous a-pyridone have been studied in various solvents. There is a limited relationship of rate to the position of the CT band of the dye. 

Placement of the second functional group at the 3-position of 59 takes one back through 1,5-dicarbonyl 67 to enone 68 and ketone 69, or enone 70 and ketone 71. Another plan that works back through odd (consonant) difunctional relationships passes through vinylogous ester 74 and 1,3-diketone 76 to ketone 78 and unsaturated ester 79 or ester 80 and unsaturated ketone 81. See if you can work back from 59 through 1,3-diketone 82 in a similar manner before moving on with this chapter. 

Explain why A can be deprotonated by lithium diisopropylamide (LDA) where as B cannot. Explain why this is not a breakdown of the principle of vinylogy. (Difiinctional Relationships-6)... 

Moreover, the stereoselective, direct vinylogous aldol reaction of halogenated or a-thio-substituted furanones with aldehydes was achieved by using appropriately tuned 22c as an optimal catalyst (Scheme 7.37) [61]. On the basis of analyses of the absolute configurations of the products as well as the relationship between the catalyst structure and the stereochemical outcomes, a transition state model was proposed. In this model, furanone-derived enolate would be located close to the... 

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