1,6-Michael-type reaction product

These Michael-type products are similar to structures obtained by Kotsuki [36] by cycloaddition reactions of N-sub-stituted pyrroles 94 with dimethyl acetylene dicarboxylate. If the substituent on the nitrogen is electron donating (R=Me), a primary 1 1 Diels-Alder cycloadduct 95 reacts further to give Michael-type reaction product 96 (Scheme 23). Described substituent influence on the susceptibility of 7-azabicyclo[2.2.1]hept-2-enes to Michael reaction is in good accord with results obtained by Scheeren [37] who has shown that the hi -pressure Diels-Alder reaction of 3-thiosubstituted N-carbomethoxypyrrole derivatives with electron-poor alkenes (12kbar, MeCN, 50°C, 16h) affords 2-thiosubstituted 7-azabicyclo[2.2.1]hept-2-enes in high yields. 

The Michael type reaction of f3/f -5-r-butyldimethysiloxy-3-phenyl-l//-pyrrolo[l,2-c oxa2ole with nitroethylene proceeds in the presence of Lev/is acid to give the alkylated product in good chemical yield and diastereoselecdvity In the case of nitroethylene, the Diels-Alder type transition state is favored to give the ryu-adduct selectively fEq 4 72 ... 

The Michael-type reaction of an anion (generated from compound 77) with ethyl crotonate yielded the corresponding ester 78 in 82% yield (Scheme 19). Alkylation of compound 77 with benzyl bromide afforded derivative 79 in 85% yield. The attempted reactions of the anion with oxiranes and trimethylsilyl chloride did not lead to the expected substitution products and the starting oxadiazoles were recovered in 70-80% yields <2001ARK101>. 

The attack by the thiolate anion on the N-oxide oxygen of 62 produces the intermediate sulfenic acid derivative 65, which, in the presence of thiols, further reacts with the thiolate anion, to give the oxime 66, which has been isolated among the reaction products. By contrast, spontaneous loss of the halide anion from 65 affords the ni-troso intermediate 67 that, by losing NO and the thiyl radical directly, or through 68, produces the a-nitrosoolefm 69. By a Michael type reaction with water this last product immediately yields the final oxime 70, which has been isolated among the reaction products. 

Cyclopropanation reactions of chloroalkanes with jt-deficient alkenes under basic phase-transfer catalysed conditions have been observed. Thus, for example, chloroacetic esters and chloroacetonitriles undergo Michael-type reactions with acrylic esters and acrylonitriles, the products of which cyclize to give cyclopropanes (see Section 6.4). 

Substitution of the acetate group at the C-3 position of the /3-sultam 105 can occur by reaction with silyl enol ethers in the presence of zinc iodide or zinc chloride. When the diazo compound is used, after desilylation with tetrabutyl-ammonium fluoride (TBAF), photochemical cyclization gives the bicyclic /3-sultam 106 as a mixture of two cis/ fra -diastereoisomers. When silyl enol ethers derived from cyclic ketones are used, the substitution product is stabilized by a retro-Michael-type reaction leading to open-chained sulfonamides 107 (Scheme 31) <1997LA1261>. 

Triphenylarsine oxide reacts with a number of electrophilic acetylenes having electron-withdrawing substituents in what are, in effect, reverse-Wittig reactions, thereby providing stable arsonium ylides (equation 31) Reaction is presumably initiated by Michael-type reaction of the oxide with the alkyne, as exemplified in equation 32. As would be expected from such a mechanism, use of an unsymmetric alkyne, as in the foregoing example, results in virtually regiospecific attack by the oxide to give the product shown. 

Bismuth chloride (16 mg, 0.05 mmol) and dry dichloromethane (3 ml) were placed in a 50-ml two-necked flask under nitrogen. An aldehyde (1.1 mmol) and a silyl enol ether (1.0 mmol) were added sequentially and the resulting reaction mixture was stirred at room temperature. The reaction was quenched with methanol/1 M HCl (10/1, 0.1 ml), water (10 ml) is added, and the product was extracted with dichloromethane (10 ml) three times. After drying, the solvent was removed in vacuo to leave a crude product, which was purified on thin layer chromatography to afford the corresponding aldol in good yield. A similar procedure was also applicable to the Michael-type reaction [91BCJ990]. 

Treatment of the 5-arylidene derivatives of l,3-diphenyl-2-thiohydantoin with malononitrile affords tetrahydropyrano(2,3-d)imidazoles (110), while 3-phenyl- or unsubstituted 2-thiohydantoins originate pyrrolo(l,2-c)imidazoles (111). These products are also obtained in a Michael-type reaction of 2-thiohydantoins with activated nitriles.282... 

The major adducts formed when phenanthridine is allowed to react with dimethyl acetylenedicarboxylate have been reformulated. - An initial Michael-type reaction gives the zwitterion (206) and succeeding reactions depend on the nature of the solvent. Adduct (207) is formed in anhydrous methanol by the addition of a proton and methoxide ion, while in benzene nucleophilic attack on the carbonyl group of a second ester molecule and subsequent cyclization provides 208. Alternatively, reaction at the triple bond of a second molecule of ester followed by ring closure of the new zwitterion gives 209. Other products related to 207 arise if the methanol contains water. 6-Methylphenanthridine with dimethyl acetylenedicarboxylate in benzene gives a mixture of the azepine (210) and tetramethyl 9a-methyl-9aA-dibenzo[a,c]quinolizine-6,7,8,9-tetracarboxylate. The... 

Treatment of pristinamycin IIa with meta-chloroperbenzoic acid afforded a compound to which the structure (79) was initially assigned, resulting from epoxidation of the more substituted double bond (12,13-C). This material did not display chemical properties characteristic of an epoxide as the assumed epoxide moiety remaining after treatment with nucleophilic reagents. Michael-type addition products on the dehydroproline ring were observed after treatment with thiols or amines (see Sect. 5.4.5). 2D-NMR analysis of the product from reaction of pristinamycin IIa with mCPBA showed that a transannular oxidative cyclization had taken place leading to formation of (80). The reaction can be considered to involve initial epoxidation of the 12,13-double bond followed by an intramolecular nucleophilic attack by the 37-hydroxy of the enol ether (Scheme 19). A similar transannular oxidative cyclization reaction has been reported for the reaction of l,5-dimethylcyclooct-4-en-l-ol with meta-chloroperbenzoic acid [125]. 

Enamines, the products of the acid-catalyzed addition of secondary amines to aldehydes or ketones, can be viewed as weakly nudeophihc enolate anions. Enamines react with a,p-unsaturated carbonyl systems in a Michael-type reaction, introducing new carbon-carbon bonds adjacent to the carbonyl group. Endocyclic enamines, such as pyrroHnes and tetrahydropyridines, are useful for the synthesis of complex heterocycHc compounds, as found in many alkaloids (Scheme 3.19). 

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