Ring-opening addition

The Zincke reaction is an overall amine exchange process that converts N- 2,A-dinitrophenyl)pyridinium salts (e.g, 1), known as Zincke salts, to iV-aryl or iV-alkyl pyridiniums 2 upon treatment with the appropriate aniline or alkyl amine. The Zincke salts are produced by reaction of pyridine or its derivatives with 2,4-dinitrochlorobenzene. This venerable reaction, first reported in 1904 and independently explored by Konig, proceeds via nucleophilic addition, ring opening, amine exchange, and electrocyclic reclosure, a sequence that also requires a series of proton transfers. By... 

Keywords epoxide, stereoselective, addition, ring opening, gas-solid reaction... 

Scheme 7.18 Fe-catalyzed conjugate addition—ring opening of oxanorbornenes.

Gyclobutanones reacted with arylboronic acids in the presence of a rhodium(i) complex to afford butyrophenone derivatives via addition-ring-opening process (Equation (224)).991 On the other hand, the addition-/ -hydride-elimination process provided a direct method for synthesizing ketones from aldehydes and arylboronic acids.992... 

Quinazoline is transformed into quinoline derivatives 5 or 6 on treatment with active methylene compounds in the absence of a base catalyst or with carboxylic acid anhydrides. The possible mechanism involves an addition, ring opening between the 2- and 3-positions and a ring-closure sequenceor an addition, ring opening between the 3- and 4-positions and a ring-closure sequence. All possible mechanisms involve 4-substituted 3,4-dihydroquinazoli-nes formed by addition to the 3,4-double bond of quinazoline (cf p 165) as intermediates. ... 

In addition, ring-opening of the CsHjo ions was found in cyclo-CjHjo-NO mixtures which lead to pentene-2, presumably through the charge-transfer reaction with NO. Pentene-2 was not a product at 1236 or 1470 A, for similar mixtures. The presence of CsHs ions was also observed in the cyclopentane photolysis at 1048-1067 A, and has been attributed to the decomposition of hot cyclopentane ions, viz. 

The anions generated from substituted ethyl acetylacetates 15 and related compounds reacted with (1 -ethoxycarbonylcyclopropyl)triphenylphosphonium tetrafluoroborate (14) to give diethyl cyclopent-l-ene-l,3-dicarboxylates 16 and 17 via 1,5-addition, ring opening with ylide formation, and intramolecular Wittig reaction.The reaction products were obtained in high yields. The location of the endocyclic double bond depended on the experimental conditions. 

Upon reaction with a sulfur ylide, 1,2,3-trimethylcyclopropenylium ion 1 was converted to thiophene derivative 2 by way of an addition-ring-opening-ring-closure process,... 

Nucleophilic addition of alkyl lithium to difluorovinyl-substituted epoxide (48) proceeds on the difluoromethylene carbon via the addition-ring opening pathway [16]. However, trimethylaluminum reagent transfers the methyl group at the carbon remote from the difluorinated carbon of 50 presumably via the Lewis acid catalyzed ring opening-addition mechanism as shown in Scheme 2.26. 

Moreover, thioketalization in the presence of BF3 etherate induced 211 to undergo addition-ring opening to afford olefin 212 regioselectively and in high yield, Eq. 128. This product was subsequently converted into damsin [186]. 

Lautens examined the reaction of cuprates with [3.2.1] oxabicydic substrate 297 and found that the major reaction pathway is an SN2 addition-ring opening, but contrary to the usual syn opening, an anti addition of the nucleophile was observed. Minor products due to anti-SN2 addition to the olefin and addition to the carbonyl group were also obtained, Eq. 196 [222]. 

The conversion of 1,3-dimethylnracil into a mixture of iV,Ai -dimethylurea and the disodium salt of formylacetic acid begins with the addition of hydroxide at C-6. The propensity for uracils to add nucleophiles can be pnt to synthetic nse by reaction with double nucleophiles, such as ureas or guanidines, when a seqnence of addition, ring opening and reclosure can achieve (at first sight) extraordinary transformations. 

Furans continue to be useful synthons for pyridazine syntheses. A detailed investigation of the reaction between ethyl 2-methoxy-2-methyl-3-oxofuran-4-carboxylate (47) and hydrazines revealed that, depending upon reaction conditions, compound 49, a mixture of 48 and 49 or, in addition to these, also 50, is obtained.172,173 Similarly, ethyl 5-nitrofuran-3-carboxylate and hydrazine yield a pyridazine, probably by addition, ring opening of the furan, and recyclization [Eq. (12)].174 Another synthesis involves electrolytic methoxylation of a furan derivative and subsequent treatment with hydrazine.175... 

Dihydroxyiation of epoxides can be carried out with syn stereospecificity using OSO4 as the active oxidant. The reaction occurs by a cycioaddition mechanism. Epoxidation is aiso a stereospecific syn addition. Ring opening of epoxides by hydroiysis aiso ieads to diois. This is usuaiiy an anf/addition with inversion of configuration at the site of nucieophiiic attack, ieading to overaii anf/dihydroxyiation. 

Write a mechanism for the reaction of glycine with N-carboethoxyphthalimide involving a sequence of carbonyl addition, ring opening, ring closure and elimination. Would you expect a similar reaction with L-phenylalanine to yield the L, the D, or the D,L-product ... 

Comparable addition/ring openings can be observed with l-alkoxypyridi-however prior acylation at the A -oxide oxygen before addition of... 

General procedure for rhodium-catalyzed enantioselective addition/ring opening of cyclobutanonef- ... 

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