Cycloadditions copper® chloride

Conjugate addition, 34-5, 51-2,53, 132, 133 Conjugate hydroxymethylation, 59-60 Copper(n) bromide, 54 Copper([) chloride, 120 Copper(n) chloride, 120 Copper(i) cyanide, 7,52, 53 Copper(i) iodide, 54 Corey s internal quench, 104 Cyanohydrin trimethylsilyl ether, 137 Cycloaddition. 34,112 Cydobutane-l,2-dione, 135 Cyclohept-2-dione, 135 Cyclohex-2-enone, 52,123 Cyclohcxa-1,3-diene, 26 Cyclohexane carboxaldehyde, 22-3,69 73,78... 

The Kinugasa reaction has been used as well for the asymmetric synthesis of P-lactams 25 via cycloaddition between chiral oxazolidinyl propynes and nitrones, in the presence of copper chloride <02TL5499>. 

An example of complexation of Ji bonds is illustrated in the isomerization reaction shown in Sch. 39. Use of copper chloride enables the efficient conversion of the cis olefin 168 to the trans olefin 169 [77]. (CuOTf)2(C6Hg) can be readily prepared (or purchased) and has been used for [2 + 2] photocycloaddition. An example of norbor-nene dimerization is shown below in which the Cu(I) forms a n complex with two molecules of the olefin and enables a facile cycloaddition.[51]... 

Azole approach. 5,8-Dihydro derivatives of this ring system (734) are known. The latter can be prepared by [ 4+ 2] cycloadditions of l,3,4-thiadiazole-2,5-dione (723) and a 1,3-diene. The former is highly reactive and is generated in situ by oxidation of 1,3,4-thiadiazolidine-2,5-dione with copper(II) chloride or LTA (74JOC2951). 

Possible competitive reactions (e.g., cycloadditions on the double bond) proceed only very slowly with diazotoluene dibenzyl ether is produced by the reaction with water so that strictly anhydrous conditions are not necessary. Similarly, the presence of traces of water does not interfere with the esterification with the aid of N,N -dicyclohexyl-0-benzylisourea, which reacts with water with the production of benzyl alcohol. The reagent is synthesized from dicyclohexylcarbodiimide and benzyl alcohol with copper(I) chloride as the catalyst. The esterification proceeds according to Scheme 5.16. 

The cycloaddition of ethoxycarbonyl azide to racemic O-acetyl cyanohydrin 21 was performed either at 40 °C in acetone or at room temperature and without solvent in the presence of a metal salt (zinc(II) acetate, nickel chloride or copper(I) cyanide) as catalyst54. The required dihydro-triazole 22 (isolated from the 2 1 mixture of regioisomers) was directly converted to the jS-acetoxy amine via migration of the endo-acetoxy group. The Ivans relationship of the hydrogen atoms at C-5 and C-6 was deduced from ll NMR. 

Dehydrohalogenation of amide chlorides affords a-chloroenamines, which undergo cycloaddition with IV-diphenylmethylaldimines to furnish azetidinium salts (303 equation 161). From these salts the diphe-nylmethyl group can be removed by hydrogenation, subsequent deprotonation yields 2-amino-1-aze-tines. The addition of primary or secondary amines to nitrilium salts gives rise to formation of amidinium salts and amidines respectively, e.g. (304 equation 162). In a similar reaction from copper(I) imidazolide, r-butyl bromide and nitriles amidines (305 equation 163) were prepared. ... 

The Staudinger ketene cycloaddition was utilized as the key reaction in the synthesis of a number of bakkane natural products in the laboratory of A.E. Greene. Dichloroketene was generated in situ from trichloroacetyl chloride by zinc-copper alloy in the presence of phosphorous oxychloride. The [2+2] cycloaddition between dichloroketene and 1,6-dimethylcyclohexene gave the product in high yield and excellent regio- and diastereoselectivity. The cycloadduct was successfully converted to (+)-bakkenolide A. 

The synthesis of unnatural (+)-mesembrine (387) through the asymmetric synthesis of methyl (i )-l-[(3,4-dimethoxy)phenyl]-4-oxocyclohex-2-enyl acetate (390) by cycloaddition of enantiomerically pure vinyl sulfoxide with dichloroketene has been performed 189) (Scheme 43). Vinyl sulfoxide 388 [prepared by conjugate addition of enantiopure acetylenic sulfoxide with (3,4-dimethoxy)phenylcopper] reacted with trichloroacetyl chloride in the presence of freshly prepared zinc-copper couple in THF at 0°C to produce a mixture of mono- and dichloro lactones 389. Reduction of 389 with zinc in acetic acid followed by cyclization and methylation afforded methyl IR-[(3,4-dimethoxy)phenyl]-4-oxocyclohex-2-enyl acetate (390), treatment of which with methylamine brought about amidation and concomitant intramolecular Michael addition to provide 2-oxo-mesembrine (391). Successively, 391 was transformed to (+)-mesembrine (387) in 79% yield (three steps ketalization of an oxo group, reduction of lactam, and deketali-zation)(/S9). 

A more recent development in the generation of oxyallyl cations from polybromoketones has been the use of diethylzinc [27], This procedure is convenient and amenable for the large-scale syntheses of oxabicyclic compounds. In addition, the combination of cerium (III) chloride and tin (II) chloride has been very effective in inducing the [4 + 3] cycloaddition between furan and 2,4-dibro-mopentan-3-one [28]. Sonication has also been observed to improve yields in cycloadditions promoted by zinc-copper couple [29]. 

Due to their tendency to undergo side reactions and the lack of stereospecificity, free methylene or alkylcarbenes, as generated from diazoalkanes by photolysis or thermal nitrogen extrusion, are of minor synthetic importance for [2 4- 1] cycloadditions. However, transition metal catalysis, most commonly with copper or palladium compounds, offers a convenient solution to this problem (Vol. E19b. p 278)s. Probably the most active catalyst is copper(I) trifluoromcthanesulfonate9. The simple diastereoselectivity of these reactions is often negligible, as demonstrated by the copper(I) chloride or palladium(II) bis(benzonitrilo)dichloride promoted cyclopropanation of phenylethene with diazoethane10. 

Cyclobutenones are obtained by the cycloaddition of dichloroketene (from trichloroacetyl chloride and zinc-copper couple) to alkynes, followed by dechlorination of the resulting dichlorocyclobutenones with zinc. The preparation of 3-butylcyclobutenone from 1-hexyne by this method (equation 46) has been described in detail. ... 

The bismuthonium ylide 519 is converted into the annelated furans 522 on treatment with terminal alkynes in the presence of copper(I) chloride. It is suggested that the process involves the carbene 520 and the diradical 521. Intramolecular [2 + 2 + 2] cycloaddition of the triyne 523 mediated by tris(triphenylphosphine)rhodium(I) chloride gives the tetrahydrofuranobenzofuran 524. ... 

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