Vinylic substitution nucleophilic

Rappoport, Z. Hanack, M. Subramanlan, L. R. Vinyl Cations Academic Press New York, 1979. 

An ab initio study suggested that a concerted Sn2 reaction is possible in the case of unactivated substrates in which the attachment-detachment pathway is not favored by electron-withdrawing substituents, and some experimental data are consistent with this prediction Glukhovtsev, M. N. Pross, A. Radom, L. /. Am. Chem. Soc. 1994,116, 5961. 

One of the interesting aspects of nucleophilic vinylic substitution is the observation that the product often retains the configuration of the reactant, as illustrated by the reactions of (Z)- and (E)-)8-bromoethyl crotonate in equations 8.81 and 8.82. Not all reactions are stereospecific, however, and the stereochemical outcome depends on the nature of the nucleophile. 

In discussions of nucleophilic vinylic substitution, the carbon atom bearing the leaving group is commonly denoted the a carbon atom, while the other olefinic carbon atom is the /3 position. . See, for example. Silversmith, E. F. Smith, D. /. Org. Chem. 1958, 23,427. 

The nucleophile approaches the a carbon atom on a line perpendicular to the plane of the olefin. 

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The nucleophilic vinylic substitution reaction of ( )-a-haloenyne sulfones with sodium alkoxides proceeds regioselectively to give ( )-a-alkoxyenyne sulfones. These conqioimds are versatile intermediates for the preparation of iiirans (Scheme 15, <96TL7381>). 

Nucleophilic substitution, in phosphate esters, mechanism and catalysis of, 25,99 Nucleophilic substitution, single electron transfer and, 26, 1 Nucleophilic vinylic substitution, 7,1... 

Nucleophilic vinylic substitution and vinyl cation intermediates in the reactions of vinyl iodonium salts. 37, 1... 

The work of Ochiai s group on nucleophilic vinylic substitution of phenyliodonium salts (see previous section) has been extended to examining the behaviour of allenyl (aryl)iodine(III). Ratios of nucleophilic substitution to [3,3]-sigmatropic rearrangement for the collapse of allenyl(aryl)iodine(III), generated from the reactions of aryliodanes... 

Evidence for a Michael addition of a nucleophile to alkenyl(phenyl)iodonium salts at the Cp atom has now been reported for the first time. Nucleophilic vinylic substitutions of (Z)-(/3-bromoalkenyl)iodonium tetrafiuoroborates (161) and its (Z)-(/3-chloroalkenyl) analogue with sodium benzenesulfinate in THE afforded stereoselectively (Z)-l,2-bis(benzenesulfonyl)alkene (163) with retention of configuration. Intermediate formation of (Z)-[/3-(benzenesulfonyl)alkenyl]iodonium salt (162) in these reactions was established by NMR experiments in CDCI3. The formation of (Z)-(162) involves a hitherto unobserved Michael addition of benzenesulfinate anion to the alkenyliodonium salts at the Cp atom, followed by halogen extrusion. ... 

The nucleophilic vinylic substitution (S mV) of heteroatom-substituted alkylidene Meldrum s acids has been intensively studied and kinetics of the reaction <1998JOC6266, 1999CJC584, 2004JOC9248> as well as synthetic applications have been reported <19978567, 2002JHC15, 2005EJ04870> (cf. Section 8.11.4.2, Scheme 10). The preparation of the substrates and a sample application is shown in Scheme 90 <2001J(P2)1534>. 

Nucleophilic additions to alkenes 293 Nucleophilic vinylic substitution (SNV) Reactions 298 Nucleophilic substitution of Fischer carbene complexes 303 Reactions involving carbocations 309 Miscellaneous reactions 312... 

In 2008 Yang and coworkers have reported an efficient synthesis of substituted a-alkilidene-fi-lactams via aNaOH- promoted intramolecular aza-Michael addition of a-carbamoyl, a-(l-chlorovinyl) ketene-S,S-acetals and subsequent nucleophilic vinylic substitution reaction in alcoholic media (Scheme 90), [198]. 

In 1991, we reported that a nucleophilic vinylic substitution of (E)-fi-alkylvinyl-AModanes with halides (BuN4X, X = C1, Br, I) in dichloromethane, methanol, or acetonitrile at room temperature proceeds with exclusive inversion of configuration [Eq. (100)] [176,177]. This is the first clear example of a vinylic Sn2 reaction. This reaction competes with an alkyne-forming reductive syn /3-elimination. 

Numerous reactions of alkenyl(phenyl)iodonium salts leading to the formation of new C-C bond have been reported in the literature. The most important and synthetically useful reactions include the generation and subsequent cyclization of alkylidenecarbenes, alkenylation of carbon substrates via nucleophilic vinylic substitution, and transition metal-mediated coupling reactions. 

Nucleophilic vinylic substitutions of 4//-pyran-4-onc and 2,6-dimethyl-4//-pyran-4-one with a hydroxide ion in aqueous solution were calculated by the density functional theory (B3LYP) and ab initio (MP2) methods using the 6-31+G(d) and 6-31G (d) basis sets. The aqueous solution was modelled by a supermolecular approach, where 11 water molecules were involved in the reaction system. The calculations confirmed a different addition-elimination mechanism of the reaction compared with that in the gas phase or non-polar solution. Addition of OH- at the C(2) vinylic carbon of the pyranone ring with an activation barrier of 10-11 kcalmol-1 (B3LYP) has been identified as the rate-determining step, in good quantitative and qualitative agreement with experimental kinetics. Solvent effects increase the activation barrier of the addition step and, conversely, decrease the barrier of the elimination step.138... 

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