Addition of enamines

At reflux, tetrahydrafuran slowly adds to terminal perfluoroalkylethylenes, perfluoroalkylacetylenes, and ethyl perfluoroalkylpropynoates [25] (equation 18) By contrast, the ionic addition of enamines to hexaJluoro-2-butyne is exothermic and gives dieneamines that, on acidic hydrolysis, yield fluoroalkenyl ketones [26] (equation 19)... 

The Michael addition of enamines to nitroalkenes proceeds with high Yyn selectivity. The Yyn selectivity is explained by an acyclic synclinal model, in which there is some favorable interaction between the nitro group and the nitrogen lone pair of the enamine group CEq. 4.67i. Both Z- and E-nitrostyrenes afford the same product in over 90% diastereoselecdvity. 

Addition of ( )-enamines 3, derived from aldehydes and ketones, to various benzylideneimini-um salts 2 has been investigated. The reaction exclusively gives the Mannich bases anti-4 in good to excellent yield (72-94%). Therefore, this method provides an efficient and highly stereoselective route to /i-amino ketones and aldehydes1415. 

A high degree of syn selectivity can be obtained from the addition of enamines to nitroalkenes. In this case, the syn selectivity is largely independent of the geometry of the acceptor, as well as the donor, double bond. Next in terms of selectivity, are the addition of enolates. However, whether one obtains syn or anti selectivity is dependent on both the geometry of the acceptor and the enolate double bond, whereas anti selectivity of a modest and unreliable level is obtained by reaction of enol silyl ethers with nitroalkenes under Lewis acid catalysis. 

High syn selectivity can be obtained from the addition of enamines to nitroalkenes. The reaction of 4-(1-cyclohexenyl)morpholine with ( )-l-bromo-4-(2-nitroethenyl)benzene gives, after acid hydrolysis, exclusively the. ryw-adduct, the relative configuration of which was unequivocally... 

Like the similar cycloaddition of ketenes to alkenes (15-61), most of these reactions probably take place by the di-ionic mechanism c (p. 1078). P-Lactams have also been prepared in the opposite manner by the addition of enamines to isocyanates ... 

Addition of ketenes to imines addition of enamines to isocyanates... 

Another pyrrole synthesis based on intramolecular substitution of the nitro group by amino function is presented in Eq. 10.7, in which the Michael addition of enamines to nitroalkenes is used.9... 

All of these reactions proceed in a similar pathway which involves the Michael type additions of enamines to nitroalkenes or addition of nitroalkanes to imines and cyclization. This process has been achieved by solid-phase variation (Scheme 10.2).14... 

The 1,2,4-triazine ring is an ambident electrophile, and reacts with enamine-type nucleophiles. For example, addition of enamine 78 to a solution of triazine 77 in acetic anhydride furnished the pyrrolotriazine 31 (Equation 24) <2003TL2421>. 

In related asymmetric Michael-additions of enamine (206) and 2-aryl- 1-nitro-ethylenes, only one of the four possible enantiomerically pure diastereomers was formed 204). Hydrolysis of the crude primary products furnished a-alkylated cyclohexanones of > 90 % enantiomeric excess 204). 

Addition of ketenes to imines addition of enamines to isocyanates 8-17 Reaction between cyclic ketones and hydrazoic acid (Schmidt)... 

The addition of enamines to l-nitroso-2-naphthol results in TV-hydroxy-1,4-oxazines 380 (equation 156) but the reaction could not be extended to 0-nitrosophenols185. 

Conjugated 2-alkoxy-6-amino-l-metalla-l,3,5-hexatrienes of type M= C(OR) — C=C—C=C(NR2) are most easily accessible by addition of enamines to alkoxy(l-alkynyl)carbene complexes in a broad array of different substituents. Due to the highly unsaturated character of such compounds a variety of transformations into organic products can be anticipated. Since... 

R. Divinyl Enamino Carbene Complexes (= 4-Enamino-1-metalla-1,3-dienes) by N-Addition of Enamines... 

The Michael addition of enamines to a,p-unsaturated ketones may be coupled with intramolecular aldol condensations to produce cyclic ketones. This sequence of reactions is an alternative approach to traditional Robinson annulations (Scheme 3.22). 

For additions of enamines, enol ethers and isonitriles see text. 

The addition of enamines to cyclopropenes in a [2 + 2] process to give a cyclobutane has been applied in a number of natural product syntheses however, in many cases, a second product was a ring-opened ketone. 

The 1,4-conjugate addition of enamines to the 4-phosphorylated 1,2-dia-zabuta-1,3-diene (184) provides a route to substituted 1-aminopyrroles (185) which can be further converted into 1-aminopyrroles (186) by basic hydrolysis (Scheme 26). Moderate to good yields of 2,6-diphosphonylated-l,2-dihyd-ropyridines (187) have been obtained in a one-pot reaction from either 1,4-dihydropyridines or pyridinium salts (Scheme 27). ... 

Interestingly, enamines attack the terminal olefinic carbon of l,l-bis(ethoxycarbonyl)-2-vinylcyclopropane (42), with ring opening of the cyclopropane ring, in contrast to sodiomalonic ester which attacks the more substituted cyclopropane carbon. With diethyl cyclopropylmethylideneraalonate (43) reaction occurs at the jff-carbon and the cyclopropyl ring remains intact (Scheme 27). Titanium tetrachloride catalyses the highly diastereoselective addition of enamines to 2,2-dimethoxyethyl crotonate. ... 

The enaminone 124 on acylation with acryloyl chloride furnished mainly 127 by the intramolecular addition of enamine to the acrylamide moiety in initial intermediate 125 (Z = COCH = CH2). The cyclization of 127 is affected by TiCl4 to form aspidosperma alkaloid pentacyclic skeleton 128 (91T4165). 

Analogous additions were later reported by Ito and co-workers (Scheme 9) (20). The enamines for these additions were prepared from the corresponding aminals using a mild base in the presence of trimethylsilyl chloride. In turn, the aminals used are available from (— )-ephedrine and (S)-prolinol. The byproduct amine hydrochloride was removed either by distillation or by precipitation from a benzene solution. Enamines prepared by this method were found to be unreactive toward unsaturated carbonyl compounds in a variety of solvents. Importantly, it was found that use of a mild Lewis acid such as anhydrous MgCl2 or ZnCl2 in THF promoted the reactions. Thus, the addition of enamines 9.1 and 9.2 to methyl acrylate is achieved. Of the two enamines, the proline-derived 9.1 is the more effective auxiliary. The... 

P,P] Risaliti and co-workers in 1966 reported the stereoselective additions of enamines derived from cyclohexanone and morpholine, piperidine, and pyrrolidine to / -nitrostyrene (Eq. [1], Scheme 15) (34). The less-substituted enamines of the general structure 15.1 were isolated prior to hydrolysis. The location of the double bond of 15.1 was established by H-NMR spectroscopy and by addition to diethyl azodicarboxylate. The... 

The enantioselective Michael addition of enamines derived from / -tetralone and proline methyl ether to nitrostyrenes has been described by Blarer and Seebach (33,45). Enamines of /1-tetralone have two potential sites of nucleophilicity, C-l and C-3 in 21.1 and 21.2(Scheme 21). For the substrates studied, attack occurs preferentially at C-3. The results of this study are summarized in Table 7 and Scheme 21. 

Narasaka reported that the titanium compound generated from TiCl2(OiPr)2 and an optically active diol in the presence of 4 A molecular sieve promoted the asymmetric addition of enamine 69 to the activated fumarate 70 [72]. Cyclobutane derivatives were formed when p,p-disubstituted enamines were employed. Titanium oxide derived from (l )-BINOL and (iPr0)2Ti=0 catalyzed the asymmetric addition of silyl thioenol ether 71 to enones [73]. The sulfur derivative ex-... 

Reactions of enamine derivatives of auxiliary 1.64 [162, 252, 262] are often disappointing, except when R = CH20SiMe3 [162], However, the alkylation of enamines derived from 1.65 (R = Me) gives satisfactory results [253, 275], as do the Michael additions of enamines of bicyclic pyrrolidine 1.68 [294],... 

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