Enamines Enaminones, cycloaddition

Triazines are generally more reactive in [2 + 4] cycloaddition in comparison with 1,2,3-tria-zines. The wide variety of dienophiles can be employed enamines, enaminones, vinyl silyl ethers, vinyl thioethers, cyclic ketene jV,O-acetals, /V-phenylmaleimide, 6-dimethylaminopentafulvene, 2-alkylidene-imidazolidines (cychc ketene aminals), cyclic vinyl ethers, arynes, benzocyclopropene, acetylenes, and alkenes like ethylene, (Z)-but-2-ene, cyclopentene, cyclooctene and bicyclo[2.2.1]hept-2-ene, hexa-1,5-diene, cycloocta-1,5-diene, diallyl ether, cyclododeca-l,5,9-triene,... 

For recent reviews on step-wise [3 + 3] formal cycloadditions leading to bridged carbocycles, pyridines or pyridones using enamines, enaminones, enol ethers, or (J-... 

In a similar process, tertiary enaminones react with alkynylcarbene complexes to give the corresponding pyranylidene complexes following a reaction pathway analogous to that described above. First, a [2+2] cycloaddition reaction between the alkynyl moiety of the carbene complex and the C=C double bond of the enamine generates a cyclobutene intermediate, which evolves by a conrotatory cyclobutene ring opening followed by a cyclisation process [94] (Scheme 49). 

Cycloaddition of ketene to enamines affords cyclobutanones, which upon distillation readily rearrange to enaminones (61JOC4775 63JOC1468). For... 

C-l,4-addition/Mannich-type cyclization through respective intermediates 303 and 304. This finding invoked historical perspectives from Prelog s work in 1949 [139] and the enamine work of Stork et al. in the 1950s [140]. With the latter case, a distinct contrast could be generalized whereby cycloadditions of a,(3-unsaturated carbonyl systems with enamines mostiy led to carbo-[3+3] cycloaddition [138], and those with enaminones, or vinylogous amides, almost exclusively proceeded down the pathway of an aza-[3+3] cycloaddition. 

The Brpnsted acid-mediated formal 3 + 3-cycloaddition reaction of /i-enaminones with cf, -unsaturated aldehydes formed tetrahydroquinolinones. The Yb(NTf2)3-catalysed 3 + 3-cycloaddition reaction of isatin ketonitrones (122) and cyclopropanes (123) yielded spiro[tetrahydro-l,2-oxazine]oxindoles (124) in moderate to good yields and good regioselectivities (Scheme 38). The Cu-catalysed 3 + 3-cycloaddition reaction of propargyl esters with cyclic enamines yielded chiral e r/o-adducts with bicyclo[ .3.1] frameworks. The catalyst was prepared by the combination of Cu(0Ac)2 H20 with a chiral tridentate ferrocenyl-PA(,(V-ligand. The cationic... 

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