Nitroolefins cyclic

Alexakis et al. showed that under optimized experimental conditions, the enantioselectivity of the Cu-catalyzed conjugate addition of dialkylzinc to cyclic nitroolefin was improved to 95% with both (A,A)-55 and (R,S,S)-29.79,79a Biphenol-based phosphoramidite ligand (S,S)-55 also provided acyclic nitroalkenes adducts with 95-96% ee.42... 

In a similar manner the reaction of tertiary enaminones and cyclic nitroolefins is used for the synthesis of a triquinan in high yield327 (equation 245). 

In Diels-Alder reactions a nitroolefin may function as an electron-deficient ene com-onent or a 1,2-dihydropyridine derivative may be used as a diene component. Both types of iactants often yield cyclic amine precursors in highly stereoselective manner (R.K. Hill, 1962 i. BOchi, 1965, 1966A). 

The regiochemical control of Pd-catalyzed hydnde transfer reacdon is much more effeedve than that of the radical denitradon, as Shown in Eq 7 98 The base-catalyzed reacdon of nitroolefins with aldehydes followed by denitradon provides a new syntbedc method of homoallyl aicohols fEq 7 99 Exomethylene compounds are obtined by denitradon of cyclic allylic nino compounds with PdfO, HGO-,H and Et- N fEq 7 100 ... 

The regiochemical control of Pd-catalyzed hydride transfer reaction is much more effective than that of the radical denitration, as shown in Eq. 7.98. The base-catalyzed reaction of nitroolefins with aldehydes followed by denitration provides a new synthetic method of homoallyl alcohols (Eq. 7.99).140 Exomethylene compounds are obtained by denitration of cyclic allylic nitro compounds with Pd(0), HC02H and Et3N (Eq. 7.100).140b... 

Initially, after the retrosynthesis of the target substrate, the starting reagents are chosen (for I, nitroolefin and two alkenes with opposite demands). Then intermediate six-membered cyclic nitronate (259) is synthesized (Scheme 3.172). 

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). 

Enamines (e.g. 377) have been shown to react with conjugated nitroolefins 378 to give mainly dihydro-l,2-oxazine A -oxide derivatives 379 as products of kinetic control (sometimes a cyclobutane ring is formed in these reactions see Section II.B). The stability of these heterocycles is largely dependent on the parent enamine and the type of substituent used on the nitro olefin as has been extensively studied by Valentin and coworkers " . Usually they open into the corresponding nitroalkylated enamines 380 (equation 82), in particular in a solution of methanol or deuteriated chloro-and often an equilibrium between the two forms is established. Stable 1,2-oxazine A -oxides have been obtained in the reaction of 2-nitro-l,3-dienes with cyclic enamines . 

Nitroolefins have proven to be excellent substrates in Michael reactions. Tin(II) enolates of cyclic ketones were found to react with 0-nitrostyrene to afford 4-nitroketones with an unprecedented anti-selectivity of up to 94% ds. (Metal enolates and enamines normally give syn-selectivity. ) The reaction could also be per-... 

Li and coworkers have studied the reaction between cyclic ketones 133 and nitroolefins 134 in the presence of the chiral pyrrolidine-thiourea bifunctional catalyst 135 (Scheme 3.41), finding that it allows an enantioselective synthesis of 3-oxa- and 3-azabicyclo[3.3.1]nonan-9-one derivatives 136, probably via a domino process comprising allylic displacement and Michael reactions as the key steps [90],... 

The first amine-catalyzed Diels-Alder reaction of a,(i-unsaturated carbonyl compounds as dienes involving in situ enamine activation with chiral amine 29 through raising the diene HOMO energy was accomplished by Barbas and coworkers in 2002 with moderate enantioselectivity (up to 38% ee) [17a]. In 2007, Cordova and coworkers described chiral amine 29 catalyzed enantioselective Diels-Alder reactions between a,P-unsaturated cyclic ketones and nitroolefins with up to 86% ee [17b]. Two years later, Xu and coworkers successfully disclosed a highly efficient enantioselective Diels-Alder reaction of cyclohexenones 31 with aromatic nitroolefins 32 using amine 30 as catalyst in seawater or brine to give products 32 with excellent enantioselectivities (Scheme 38.10) [18a]. Notably, sea water and brine... 

Kumaran G, Kulkami GH. Effect of the a-alkyl substituent of conjugated nitroolefins on the formation of cyclic nitronic esters vs. nitrocyclopropanes in their reaction with sulfur ylides. Synthesis 1995 1545-1548. 

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