Intramolecular nucleophilic acyl

THF) at room temperature (Scheme 18) (95T8605). The proposed mechanism for this conversion involves the abstraction of H3 by basic attack of NaH to give an enolate anion, which, via ring opening, affords the 2(5//)-furanone 61 by a straightforward intramolecular nucleophilic acyl substitution (Scheme 18) (95T8605). 

The following reaction involves a hydrolysis followed by an intramolecular nucleophilic acyl substitution reaction. Write both steps, and show their mechanisms. 

Intramolecular Nucleophilic Acyl Substitution (INAS) Mediated by 1... 

Intermolecular nucleophilic acyl substitution is a fundamental carbon—carbon bondforming reaction. In spite of its high synthetic potential, however, its intramolecular version, that is, intramolecular nucleophilic acyl substitution (INAS) is rather rare because of the intrinsic difficulties involved in carrying it out. One difficulty associated with the INAS reaction is that a reactive nucleophilic species must be generated in the presence of carbonyl functionality, and at the same time this nucleophile is expected to react only with... 

In analogy with iron-catalyzed Barbier-type reactions with Sml2 (cf. Scheme 8.5), intramolecular nucleophilic acyl substitutions (SNt) can be used to prepare cyclic ketones from esters [50]. An illustrative example is shown in Scheme 8.13 [51], Again, tris(l,3-diphenyl-l,3-propanedionato)iron(III) [Fe(dbm)3] is used as the catalyst. Compound 40 is obtained as one racemic diastereoisomer. 

One of the characteristic reactions of the Ti reagent is the intramolecular nucleophilic acylation of the titanacycle with esters, and 2,7- and 2,8-enyne esters afford interesting mono- and bicyclic skeletons [125], Titanacycle 297, formed from a, /i-unsaturated ester 296, is converted to the alkenyltitanium 300 by protonation, and the cyclopentenone 301 is formed by intramolecular acylation [126], As 297 is a tautomeric form of the Ti enolate, it reacts with electrophiles such as aldehydes to give 298, which cyclizes to 299. The a,/i-alkynic ester 302 generates the titanacycle 303 and is converted to the bicyclo[3.1.0]hexane system 305 via 304 [126]. The titanacycle... 

An interesting intermolecular version of this reaction has likewise been put forward for the preparation of seven-, eight-, and nine-mem-bered carbocycle, as illustrated with a sole example in Scheme 3 [7]. In contrast to the above, these reactions begin with a carbonyl addition reaction of chloroiodoalkanes to cyclic or acyclic keto esters leading to the formation of an intermediate lactone. An intramolecular nucleophilic acyl substitution then terminates the sequence. The example in Scheme 3 represents a simple method for the construction of the 5 8 5 tricyclic ring system. 

Solventless, Room-Temperature Diels-Alder Reaction Intramolecular Nucleophilic Acyl Substitution A Huge Increase in Molecular Complexity in a 10-mL Beaker... 

Solventless, Microwave-Assisted Synthesis of Coumarins via a Tandem Knoevenagel Condensation and an Intramolecular Nucleophilic Acyl Substitution... 

We have been particularly enamored with the development of experiments involving carbon-carbon bond formation, especially as part of tandem reactions occurring in a single container (see the Diels-Alder reaction. Figure 1). One such reaction is the synthesis of simple esters of coumarin-3-carboxylic acids via a Knoevenagel condensation between malonic esters and various a-hydroxybenzaldehydes, followed by intramolecular nucleophilic acyl substitution. This conversion, catalyzed by piperidine, has been carried out under a variety of conditions, for example, at room temperature without solvent... 

The ABC ring system of the carbocyclic skeleton of variecolin, a sesterterpenoid natural product was accomplished by G.A. Molander and co-workers. In their approach, they utilized two samarium diiodide mediated processes. First, a primary alkyl iodide was reacted with a ketone substrate in the presence of two equivalents of samarium diiodide and catalytic nickel(ll) iodide under samarium Grignard conditions. Subsequent oxidation and lactone formation provided the chlorolactone substrate. As alkyl chlorides are less reactive than alkyl bromides and iodides, the second samarium diiodide mediated process, an intramolecular nucleophilic acyl substitution, required visible light irradiation. 

Molander, G. A., McKie, J. A. Intramolecular nucleophilic acyl substitution reactions of halo-substituted esters and lactones. New applications of organosamarium reagents. J. Org. Chem. 1993, 58, 7216-7227. 

Molander, G. A., Harris, C. R. Sequenced Reactions with Samarium(ll) Iodide. Tandem Intramolecular Nucleophilic Acyl Substitution/Intramolecular Barbier Cyclizations. J. Am. Chem. Soc. 1995, 117, 3705-3716. 

Low-valent titanium alkoxide complexes have proved to be particularly useful in intramolecular nucleophilic acyl substitution (INAS) reactions. Addition of propargyl alcohol derivatives to 236 has been used as an efficient and practical method for the synthesis of allenyltitanium compounds (Scheme 43).197 Performing the reaction with a homopropargylic carbonate provides access to an alkenyltitanium compound with a lactone moiety.198 This methodology has since been extended to include olefinic carbonates and, through trapping with appropriate electrophiles such as aldehydes and iodine, affords substituted lactones.199... 

Intermolecular ketyl alkene coupling reactions have been incorporated into a cascade that ultimately affords medium sized rings [58]. Specifically, chloroalkyl ketones react with acrylates, whereupon chloroalkyl lactones are formed in situ. Photolysis of these intermediates in the presence of excess Sml2 initiates an intramolecular nucleophilic acyl substitution reaction between the halide and the lactone, creating the medium-sized ring (Eq. 50). 

Nucleophilic Acyl Substitutions. Samarium(II) iodide facilitates the highly selective intramolecular nucleophilic acyl substitution of halo esters (eqs 19 and 20). ... 

Some amino acids cannot be incorporated into proteins because they are self-destructive. Homoserine, for example, can use its side-chain OH group in an intramolecular nucleophilic acyl substitution to cleave the peptide bond and form a cyclic structure on one end of the chain ... 

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