Trapping intramolecular

Alkyl- and arylmercury(II) halides are used for the ketone formation[402]. When active methylene compounds. such as /f-keto esters or malonates are used instead of alcohols, acylated / -keto esters and malonates 546 are produced, For this reaction, dppf is a good ligand[403]. The intramolecular version of the reaction proceeds by trapping the acylpalladium intermediate with eno-late to give five- and six-membered rings smoothly. Formation of 547 by intramolecular trapping with malonate is an example[404]. 

A similar intramolecular trapping of the intermediate (511) from the photolysis of the corresponding methyl tetrazole-l,5-dicarboxylate (510) gave methyl 5-methoxy-l,2,4-oxadiazole-3-carboxylate (512). 

An intramolecular trapping variant of the Hoch-Campbell aziridine synthesis was reported by Taguchi et When 2-(l-p-chlorophenylcyclohexyl)cyclohexanone (16)... 

Finally, an ingenious synthetic sequence by Trost, Cossy and Burks201 includes a unique desulphonylation reaction that involves an electron-transfer process. The synthetic sequence uses 1, l-bis(phenylsulphonyl)cyclopropane as a source of three carbon atoms, since this species is readily alkylated even by weakly nucleophilic species. Given an appropriate structure for the nucleophile, Trost found that desulphonylation with lithium phenanthrenide in an aprotic solvent allowed for an efficient intramolecular trapping of the resultant carbanion (equation 88). This desulphonylation process occurs under very mild conditions and in high yields it will undoubtedly attract further interest. 

SCHEME 9.22 Intramolecular trapping produces a self-adduct of the quinone methide conjugate. 

The group of Nakatani introduced photochemically induced cyclization that takes advantage of a system in which a carbene generator and a carbene trap are combined in the same molecule [37]. Thus, irradiation of compound 5-105 induced a cyclization to give an intermediate carbene 5-106, which underwent an intramolecular trapping by a pericyclic 6jt electrocyclization to afford 5-107 in a very good yield of 95% (Scheme 5.21). 

Intramolecular cyclizations could also be achieved by oxidation of 57 with PCC to 65 regioselective addition of an organometallic onto the 7(2)-carbonyl carbon of 65 was followed by treatment with acid to generate the iminium cation, and intramolecular trapping of the cation by an appropriate N-2 substituent (e.g., phenylethyl substituent) <2001TA2883> or C-4 substituent (e.g., benzyl group) <2002T6163>. 

Organometallic reactions leading to condensed pyrans containing three or more rings have been achieved by cyclooligomerization processes and by intramolecular coupling. The former type of reaction is based on intramolecular trapping of o-xylylenes produced in cobalt-catalyzed cyclization... 

A series of benzisothiazolone derivatives 238 has been prepared from methylthiosalicylate 235 O60L4811>. The key cyclization step features the formation of a TV-acylnitrenium ion 237, generated by the hypervalent iodine reagent, phenyliodine(III)bis(trifluoroacetate) (PIFA). This ion cyclizes to benzisothiazol-3-one 238 upon intramolecular trapping of the thiol moiety. 

Intramolecular trapping of allyl radicals by carbon-carbon double bonds has, of course, been observed to occur readily and with high selectivity (see Sections in and IV). 

Intramolecular Trapping of Bis-N,N-Oxyiminium Cations Special y-functionalized nitro compounds (372) were constmcted with the aim of performing intramolecular trapping of bis-7V,7V-siloxyiminium cations prepared in process of double silylation of (372). Monosilylation of the latter compounds can afford different silyl derivatives (373a-c) (Scheme 3.212) (486, 487). 

In intramolecular trapping of bis-oxyiminium cations, Me3SiBr was used as the silylating agent, which makes it possible to smoothly perform silylation of primary AN (see Chart 3.20). A representative group of substrates (372) was synthesized for intramolecular trapping of cations (488). 

Selected Features of the Chemistry of N,N-Bis-Trimethylsiloxy-Substi-tuted Cyclopropanes and Dihydrofurans Scheme 3.217 shows selected features of the chemistry of compounds prepared by intramolecular trapping of bis-N,N-(trimethylsiloxy)iminium cations. 

Scheme 4.9. Lewis acid-assisted intramolecular trapping of an alkylzirconium chloride. Fc RJ 11 R2 g, R3 12 (50-77%)...

As indicated by the aforementioned examples U5-U8>5 the most useful feature of the intramolecular trapping of o-xylylenes generated from benzocyclobutenes is the control of stereochemistry so that high purity of ( )-estrone could be obtained. Subsequent molecular manipulation of synthetic estrone may give rise to alternative routes to other medicinally important steroid drugs. 

An alternative approach for generating the pentadienyl carbocation that is needed for the Nazarov cyclization has been demonstrated by de Lera and co-workers [20, 21] (Eq. 13.18). Vinylallene acetal 56 is converted to a ca 1 1 mixture of cyclopentenes 57 and 58 upon exposure to toluenesulfonic acid in acetone at room temperature. The reaction presumably involves initial generation of carbocation 59 that undergoes conrotation to give 60. Intramolecular trapping of the carbocation by the pendant hydroxyl group leads to the observed product. Depending on whether the conrotation in 59 takes place clockwise or counterclockwise, E- (57) or Z-(58) products are formed. 

Intramolecular trapping was also possible, as exemplified by the synthesis of cyclic ureas (Eq. 53) [275] and oxazolidin-2-ones [232,234] (Eqs. 54 and 55). 

Scheme 3.18. Ring-formation by intramolecular trapping of the vinylcuprates resulting from silylcupration of alkynes with magnesium silylcuprates [75a] or lithium silylcuprates (mCPBA = m-chloroperbenzoic acid) [75bj.

CPO has been applied almost exclusively as biocatalyst for the hydroxyhalo-genation. Recently, lactoperoxidase-catalyzed bromination of laurediols was reported [141,142]. In this reaction, cyclic ethers were unspecifically formed by intramolecular trapping of the carbocation with hydroxy groups (Eq. 8). 

Phosphorylated 2,3-diamino-2//-indazoles (172) are well suited for the annulation of a 1,2,4-triazole ring by a combination of an aza-Wittig and an intramolecular trapping reaction. As shown in Scheme 66, CS2 and CO2 are good reaction partners in the case of acid halides, however, no ring closure occurs, and 173 was obtained (89TL6237 90JOC4724). 

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