Intramolecular substitution nucleophilic

Diylide 1, by reaction with a phosphorus electrophile, Ph2PCl, lead instantaneously via a nucleophilic substitution and intramolecular prototropy to the formation of functionalized monoylides 10 (Scheme 11). 

Aromatic nitro compounds undergo nucleophilic aromatic substitutions with various nucleophiles. In 1991 Terrier s book covered (1) SNAr reactions, mechanistic aspects (2) structure and reactivity of anionic o-complexes (3) synthetic aspects of intermolecular SNAr substitutions (4) intramolecular SNAr reactions (5) vicarious nucleophilic substitutions of hydrogen (VNS) (6) nucleophilic aromatic photo-substitutions and (7) radical nucleophilic aromatic substitutions. This chapter describes the recent development in synthetic application of SNAr and especially VNS. The environmentally friendly chemical processes are highly required in modem chemical industry. VNS reaction is an ideal process to introduce functional groups into aromatic rings because hydrogen can be substituted by nucleophiles without the need of metal catalysts. 

The resulting polymerization is a copolymerization between the two monomers, not a homopolymerization of MMA. More importantly, this results in a slower reaction (and lower polymer molecular weight) since the carbanion derived from the ketone is not as reactive as the carbanion from MMA. Nucleophilic substitution by intramolecular backbiting attack of a... 

In summary, it would appear that the oxidation of a catecholamine probably first involves the formation of a semi-quinone radical (this can be brought about by an one-electron transfer, e.g. from Cu++ ions,14 or by photoactivation 1) which rapidly undergoes further oxidation (e.g. with atmospheric oxygen) to an intermediate open-chain quinone (such as adrenaline-quinone) and then cyclizes by an oxidative nucleophilic intramolecular substitution to the amino-chrome molecule. Whilst the initial formation of a leucoaminochrome by non-oxidative cyclization of the intermediate open-chain quinone in some cases cannot be entirely excluded at the moment (cf. Raper s original scheme for aminochrome formation72), the... 

Wrobel and Golfbiewski (67) interpreted the condensation in terms of a two stage reaction a Claisen-Schmidt condensation resulting in an amino alcohol (147) followed by nucleophilic intramolecular substitution of the OH group. Quick and Oterson (69) suggested a modification of the latter... 

The authors proposed a mechanistic explanation for these different behaviors. For the case of the free phenol cydization precursor 40a, an ionic mechanism via intermediate 44 leads to the nucleophilic intramolecular para substitution product 41a (Scheme 11). For the O-protected derivatives 40s-w, an alternative mechanism leads to the formation of the cation radical 45, which then participates in an intramolecular cydization to deliver an activated... 

In one of the last transformations in a multistep synthesis of 1,2-dihydro-8-ep/-vernolepin (43), nucleophilic intramolecular substitution at an iodomethyl group was promoted by heating an ester precursor with an equivalent of NaOAc in DMF (Equation (18)) <95TL3ii>. Molecular mechanics analysis of the precursor produced a minimum energy conformer that showed the hydroxyl substituent too distant from the iodomethyl group to have interfered with this high yield transformation. 

Both xanthones and thioxanthones are available through CsF-promoted coupling of arynes with salicylates and thiosalicylates. The synthesis proceeds through sequential intermolecular nucleophilic substitution and intramolecular electrophilic cyclisation (Scheme 39) <07JOC583>. The Pd-catalysed annulation of 3-iodoflavone with the same triflate results in the dibenzo[a,c]xanthone (Scheme 39) <07JOC223>. 

Notes-. Most used reactions are SEAr (iododemetallation) and SNAr (halogen exchange, copper assisted). SeI, unimolecular electrophilic substitution Se2, bimolecular electrophilic substitution SeAp aromatic electrophilic substitution SeI, intramolecular electrophilic substitution S l, unimolecular nucleophilic substitution 3 2, bimolecular nucleophilic substitution S Ar, aromatic nucleophilic substitution. 

A concise a-amino acid-based synthetic approach via sequential inter-molecular nucleophilic substitution and intramolecular Michael addition reactions starting from MBH acetates has also been described to synthesize disubstituted [l-4]oxazepin-2-ones 821. Such a synthetic method was operationally simple under ambient conditions, and gave 81-93% yields of the target [l,4]oxazepin-2-ones (Seheme 4.236). 

Oxygen nucleophiles Intramolecular oxa-Michael cyclization of a,/ -unsaturated carbonyl compounds (278) (e.g. thioesters, oxazolidinone imides, and pyrrole amides), catalysed by Brpnsted acids, such as camphorsulfonic acid (CSA), has been reported to afford 2,6-cis-substituted tetrahydropyrans (279) with good to excellent stereoselectivity (7 1 to >20 1 dr). The approach has been claimed to be superior to that mediated by bases and is complementary to the ruthenium-catalysed cyclization affording anal- 0 ogous products (149) discussed earlier. 

No 0-allylation is observed in formation of the six-membered ring compound 79 by intramolecular allylation of the /3-keto ester 78(15,57]. Intramolecular allylation is useful for lactone fonnation. On the other hand, exclusive formation of the eight-membered ring lactone 81 from 80 may be in part derived from the preference for the nucleophile to attack the less substituted terminus of the allyl system[58]. 

With a carboxy group on the alkyl chain of the alkylthio substituent. C-4 may be involved in an intramolecular nucleophilic substitution to give 159 (Scheme 84). 

Next in what amounts to an intramolecular Williamson ether synthesis the alkoxide oxygen attacks the carbon that bears the halide leaving group giving an epoxide As m other nucleophilic substitutions the nucleophile approaches carbon from the side oppo site the bond to the leaving group... 

Overall the stereospecificity of this method is the same as that observed m per oxy acid oxidation of alkenes Substituents that are cis to each other m the alkene remain CIS m the epoxide This is because formation of the bromohydrm involves anti addition and the ensuing intramolecular nucleophilic substitution reaction takes place with mver Sion of configuration at the carbon that bears the halide leaving group... 

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