Nucleophilic opening

Electrophiles, such as C—Hal functions, contained in side chains may be well positioned for interaction with ring heteroatoms. Thus, Af-t-butyl-2-tosyloxymethylaziridine in ethanol displaces tosylate ion from the side chain, and nucleophilic opening of the resulting azabicyclobutanonium ion by solvent gives 3-hydroxy- and 3-ethoxy-azetidine (Section 5.09.2.3.2). 

These give the products expected from electrophilic attack on oxygen by the electrophilic reagent atom, followed by nucleophilic opening of the cyclic oxonium ion (e.g. 42 Scheme 29) <64HC(19-1)436). 

Nucleophilic attack on ring carbon (Scheme 39) is the most important reaction of these compounds (the electrophile may bond to oxygen either before or after nucleophilic attack). For vinylogous nucleophilic opening by 5n2 attack on ethenyloxiranes see Section 5.5.3.8. 

Nucleophilic opening of oxiranes to give ultimately 1,2-diols is usually effected without isolation of the oxirane oxiranation (epoxidation) of alkenes with unbuffered peroxy-ethanoic acid or hydrogen peroxide in methanoic acid (Section 5.05.4.2.2(/)) tends to give monoesters of 1,2-diols (e.g. 53), which can be hydrolyzed to the diols (Scheme 46). 

The preceding mechanism of the nucleophilic opening of the isoxazole ring is in accordance with the kinetic evidence of Pino... 

Obviously, the ionic liquid s ability to dissolve the ionic catalyst complex, in combination with low solvent nucleophilicity, opens up the possibility for biphasic processing. Furthermore it was found that the biphasic reaction mode in this specific reaction resulted in improved catalytic activity and selectivity and in enhanced catalyst lifetime. 

Steps 1-2 of Figure 27.14 Epoxide Opening and Initial Cyclizations Cyclization is initiated in step 1 by protonation of the epoxide ring by an aspartic acid residue in the enzyme. Nucleophilic opening of the protonated epoxide by the nearby 5,10 double bond (steroid numbering Section 27.6) then yields a tertiary carbo-cation at CIO. Further addition of CIO to the 8,9 double bond in step 2 next gives a bicyclic tertiary cation at C8. 

Posner recently reported a very simple and fast way to activate epoxides towards nucleophilic opening by ketone lithium enolate anions by use of BF3 Et20 (1 equiv.) [73]. The application of this procedure to the nucleophilic opening of propene oxide with the lithium enolate of 2-cycloheptanone, obtained by the conjugate addition of trimethylstannyllithium to 2-cycloheptenone, afforded the stan-... 

Scheme 12.25 Nucleophilic opening of aziridinium ions with azide.

For a study on the influence of Lewis acids on the nucleophilic opening of N-acyl azir-idines vs. their rearrangement to oxazo-lines, see D. Ferraris, W. J. Drury III, C. Cox, T. Lectka, ]. Org. Chem. 1998, 63, 4568-4569. 

An indirect nucleophilic opening is depicted in Scheme 24. The functionalized vinyl aziridine 37 undergoes a Michael-initiated ring closure (MIRC) reaction upon treatment with suitable nucleophiles to give cyclopropanes with concomitant opening of the aziridine ring [34]. 

The bridging by bromine prevents rotation about the remaining bond and back-side nucleophilic opening of the bromonium ion by bromide ion leads to the observed anti addition. Direct evidence for the existence of bromonium ions has been obtained from NMR measurements.31 A bromonium ion salt (with Br3 as the counterion) has been isolated from the reaction of bromine with the very hindered alkene adamantylide-neadamantane.32... 

The mechanism of oxygen transfer is believed to involve nucleophilic opening of the oxaziridine, followed by collapse of the resulting X-sulfonylcarbinolamine.252... 

The following is an example for a sequential one-pot epoxide formation/nucleophilic opening process using (S)-4-(benzyloxy)-l,2-butanediol, iV-(p-tohienesulfonyl)-imida-zole, and 2-lithio-l,3-dithiane ... 

Stereocontrolled nucleophilic opening at the C 1-position of epoxides to furnish substituted piperidine 182 was accomplished through the use of Lewis acids TMSOTf or Sc(OTf), <06CC2156>. 

Compound 254 can be considered as a masked /3-ketonitrile. Treatment of the latter with hydrazine hydrate led to nucleophilic opening and recyclization to give the triazolopyridine 255 along with 256 which was converted to the [1,2,4] triazolo[4,3-<2 pyridine 257 (Scheme 62) <2004JHC549>. 

The in situ nucleophilic opening of thiadiazolium 98, prepared from compound 97, has been described (Scheme 6) <2001JP1662>. 

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