Intramolecular displacement

Stereochemical nonrigidity is ubiquitous with seven and higher coordinated complexes because the geometries associated with them are easily interconverted by relatively small atomic displacements. Intramolecular rearrangements are complex but their understanding is helped considerably, but not solved, by nmr techniques. ... 

Convertible isocyanide reagent 66 allows a mild and chemoselective in situ post-Ugi activation of the isonitrile bom amide with simultaneous deprotection of the nucleophilic amine, that is, liberation and activation of two Ugi-reactive groups, if desired also under subsequent lactam formation [33]. Another recently introduced convertible isocyanide, l-isocyano-2-(2,2-dimethoxyethyl)-benzene 73, was shown effective by Rhoden et al. In the course of this short sequence, a hydrolytically labile W-acylindole 78 is formed, which is displaced intramolecularly by the amine portion of the former Boc-protected amino acid 75 (Scheme 13). 

The first step of the Provost reaction is the reaction of the alkene with iodine to form the cyclic iodonium ion. Next, the iodonium ion is stereospecifically opened by the silver carboxylate to form the corresponding frans-1,2-iodo carboxylate. The iodine is displaced intramolecularly by the carbonyl group of the carboxylate (anchimeric assistance) to form a cyclic cationic intermediate. In the absence of water, this cation is opened with the inversion of configuration by the second equivalent of silver carboxylate to afford the frans-1,2-dicarboxylate. However, in the presence of water Woodward-Brutcher modification) the common intermediate is converted to a c/s-orthocarboxylate which is hydrolyzed to the corresponding c/s-1,2-diol. 

Alkylation of lithiated l-(l-ethoxyprop-2-enyl)benzotriazole leads to enones after hydrolytic removal of the heterocycle addition of the lithiated species to cyclohexenone then hydrolytic cleavage of the heterocycle prodnces an nnsaturated l,4-diketone. ° Addition of the same anion to methyl but-2-enoate generates an anion in which the benzotriazole is displaced intramolecularly and a cyclopropane resnlts. ... 

The mechanism of the Ramberg-Backlund reaction is rather straightforward. When a-halosulfone 1 is treated with a strong base, deprotonation rapidly takes place to give a-anion 3, which undergoes a backside displacement (intramolecular nucleophilic substitution, SNi) to provide thiirane dioxide 4 (also known as episulfone) as the key intermediate.10 The Swi reaction with loss of halide is the rate-limiting step. Finally, the unstable 4 releases sulfur dioxide and the ring strain to deliver alkene 2. 

Quenching the alkoxyenolate derived from 3 with iodine gives an intermediate iodide 229 with 2 1 anti syn selectivity. Upon warming, iodine is displaced intramolecularly by the hydroxy group, thus forming epoxide 230 in satisfactory yield [79]. 

Epoxide 550 is prepared from 538 by converting the primary hydroxyl to a suitable leaving group that can be displaced intramolecularly by the secondary hydroxyl group. Tosylation of 538 with tosyl chloride in pyridine followed by cyclization with DBU gives 550 [131]. Alternatively, treatment of 538 with NBS followed by sodium hydroxide affords 550 in 60% overall yield [133]. In both cases the epoxide is obtained with >98% optical purity (Scheme 79). 

The amide oxygen displaces intramolecularly the chlorine atom. 

The liberated alcohol, which exists as an alkoxide under the basic reaction conditions, displaces intramolecularly the iodide, producing a tetrahydrofuran. 

The resulting nitrogen miion displaces intramolecularly the chloride, yielding an aziridine. 

The alcohol on position 2 displaces intramolecularly one of the mesylates, leading to a tetrahydrofuran. 

The ester carbonyl displaces intramolecularly the mesylate, yielding a carbocation that is happed by edianol. 

The resulting carbanion displaces intramolecularly the bromine atom, producing a very strained cyclopropanone. 

By Nucleophilic Displacement — Intramolecular cyclization of urethane 12 followed by hydrolysis provided l,6 anhydro-2-amino-2-deoxy-4-0 methyl-P-D-mannopyranose 13 (Scheme 3). 

In the reaction of aryl and alkenyl halides with 1,3-pentadiene (248), amine and alcohol capture the 7r-allylpalladium intermediate to form 249. In the reactions of o-iodoaniline (250) and o-iodobenzyl alcohol (253) with 1,3-dienes, the amine and benzyl alcohol capture the Tr-allylpalladium intermediates 251 and 254 to give 252 and 255[173-175]. The reaction of o-iodoaniline (250) with 1,4-pen tadiene (256) affords the cyclized product 260 via arylpalladiuni formation, addition to the diene 256 to form 257. palladium migration (elimination of Pd—H and readdition to give 258) to form the Tr-allylpalladium 259, and intramolecular displacement of Tr-allylpalladium with the amine to form 260[176], o-Iodophenol reacts similarly. 

The addition of nucleophiles to double and triple bond systems is often a convenient way of effecting an intramolecular ring closure. Addition to cyano groups has received considerable attention, as in addition to ring formation it provides a convenient method for the introduction of an amino group. Reaction of methyl Af-cyanodithiocarbimidate with Af-methylaminoacetonitrile resulted in displacement of methanethiol and formation of (314). Sodium ethoxide treatment in DMF converted (314) into a 4-amino-5-cyanoimidazole... 

Preparative routes to aziridines and 1-azirines are derived from cycloelimination processes in which one, and sometimes two, bonds are formed directly to the nitrogen atom (Scheme 1). For aziridines these include the two intramolecular cyclization pathways involving either nucleophilic displacement by the amine nitrogen (or nitrenium anion) on the /3-carbon (route a) or nucleophilic displacement by a /3-carbanionic centre on the amine nitrogen... 

S-Substituted thiiranium ions react with secondary amines to give ring-opened products. Nitriles also react with thiiranium ions, probably via an open carbenium ion whose formation is favored by increasing the polarity of the medium by the addition of lithium perchlorate (Scheme 79) (79ACR282). An intramolecular displacement by an amide nitrogen atom on an intermediate thiiranium ion has been invoked (80JA1954). 

An intermolecular carbenoid reaction followed by intramolecular displacement of acetate gives the clavulanic acid derivative (112) in one step from 4-acetoxyazetidin-2-one (91) (80CC1257). Carbene-induced reactions of penicillins and cephalosporins have been reviewed (75S547, 78T1731). 

Inter and Intramolecular nucleophiKc displacement o< alcohols wHh inversion by means of cHethyi azo cartMxylate (DEAD)-triphenylphosphine and a nucleophile. Also dehydration, esterification of alcohols or alkylallon of phenols,... 

The Raman spectrum in Fig. 10 for solid Ceo shows 10 strong Raman lines, the number of Raman-allowed modes expected for the intramolecular modes of the free molecule [6, 94, 92, 93, 95, 96, 97]. As first calculated by Stanton and Newton [98], the normal modes in molecular Ceo above about 1000 cm involve carbon atom displacements that are predominantly tangential... 

Figure 3.11 shows the relative reactivity as a function of ring size for two other intramolecular displacement reactions, namely, conversion of ethers from ca-bromoalkyl monoethers of 1,2-dihydroxyben-zene. 

Intramolecular Nucleophilic Displacement of Fluorine Hudlicky, M Isr J Chem 17, 80-91 68... 

Base-promoted cyclization of vicinal halohydrins (Section 16.10) This reaction is an intramolecular version of the Williamson ether synthesis. The alcohol function of a vicinal halohydrin is converted to its conjugate base, which then displaces halide from the adjacent carbon to give an epoxide. 

This sulfonate, prepared from B0CNHCH2CH2C(CH3)2CH20H and the sulfonyl chloride (Pyr, 100% yield) is cleaved by initial BOC cleavage to release the free amine after pH adjustment to 7-8. Intramolecular displacement occurs to release the sulfonate and a pyrrolidine. ... 

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