Cyclic /3-ketoenamines

Reaction of cyclic / -ketoenamines with diethyl diazene dicarboxylate is observed to yield Michael-type adducts85,86 (equation 61). For aromatization of the products see Section II.A.5. In contrast, the corresponding a-ketoenamine reaction leads to heterocyclic Diels-Alder adducts (see Section IV). 

A,iV-Dimethylformamide dimethyl acetal can be used to obtain A-benzyldihydroindo-le-7(6//)ones in good yield by reaction with a / -methyl derivative of a cyclic ketoenamine (equation 231). Apparently no other substitution in 1,2,3-position of indole is available by this method313. 

Endocyclic enamines may be combined with / -functional groups leading to cyclic -phospholene sulphide enamines (60), cyclic -ketoenamines (61), 3-(pyrrolidi-n-l-yl)-5,6-dihydro-4/f-thiopyran 1,1-dioxide (62) and 3-amino-5,6-dihydro-4/f-pyran (63). 

Ketoenamines derived from chiral cyclic amines were found to react with Grignard reagents or organolithium compounds by a 1,2-addition. Subsequent hydrolysis gives R- (or (5)-a-hydroxycycloalkanones in high enantiomeric excess. The stereochemical selectivity is caused by different structures of the intermediate formed by complexation of the different organometallic compounds320 (equation 238). 

Whereas cyclic secondary enaminones and nitroolefins mainly yield indoles in which the enamine nitrogen is incorporated into the heterocyclus (equation 242), linear tertiary a-ketoenamines are shown to react with nitroolefines at low temperature under kinetic control to give 1,2-oxazine N-oxides as [4 + 2]-cycloadducts, followed by retro-Diels-Alder reaction or rearrangement under thermodynamic control which leads diastereo-selectively to aminocyclopentenes. The reaction is called [3 + 2]-carbocyclization, apparently because the ketoenamine is reacting as a 1,3-dipole. The products are hydrolysable to polysubstituted nitrocyclopentanones with retained configuration325 (equation 243). 

Reaction of a-ketoenamines with a series of cyclic and acyclic nitroolefins gave aminocyclopentene derivatives with high diastereoselectivity, as products of kinetic control instead of the expected 1,2-oxazine N-oxides (see Section III.D.2)45,46. For example, ketoenamine 62 when reacted with cyclic nitroalkene 61 afforded 65 as a single diastereoisomer46, first through the dipolar intermediate 63 and later through the betaine-type intermediate 64. Hydrolysis of this enamine furnished the cyclopentanone derivative 66, also as a single diastereoisomer (equation 11). 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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