Involving electron-deficient

The lack of steric effects in oxidations of hydrocarbons by Cr(VI) renders D and E unacceptable. The activated complex of scheme C is non-linear and hence does not comply with the magnitude of the observed isotope effect. Two pieces of evidence are quoted which indicate A to be the more probable of the remaining two. Firstly, the p constant of —1.17 is more in agreement with that obtained for bromine atom abstraction from toluenes (—1.369 to —1.806) than those found for solvolyses involving electron-deficient carbon ( — 2.57 to —4.67) . Secondly, the correlation between the relative rates of oxidation of the series... 

Sensitized cross-dimerizations form a second group with a few examples shown in Eqs. 24—27. Most examples involve electron-deficient olefins as one addend. The reactions are again highly regioselective... 

Rigby and coworkers305,309 also performed metal mediated [6 + 4] cycloadditions of heterocyclic trienes and tropones with various dienes. In concurrence with the all-carbon trienes, the electronic nature of the diene partners generally had little influence on the cycloaddition efficiency. The only reported exceptions are the reactions of thiepin-1,1-dioxides. Lower yields were observed in the reactions involving electron-deficient dienes in comparison with the reactions with electron-rich dienes. The reaction of complex 514... 

Conjugated oximes were converted to pyrazoles in a one-pot reaction by refluxing with hydrazine and iodine in ethanol. The process proceeds via an inverse electron-demand Diels-Alder reaction involving electron-deficient heterodienes and diimide species as dipolarophiles . ... 

Let us now focus our attention on the interaction between lithium alkyls and Group III derivatives. These species are often considered to be metalates with discrete MR4 ions present, but a variety of studies show that substantial metal-anion interactions occur both in solution and in the solid state (45, 96, 131). More thorough examination of both of the structures and spectroscopic properties of these derivatives shows that they must be included in any treatment involving electron-deficient bonding. 

There are several analogies for this kind of rearrangement that involve electron-deficient carbon (Sections 8-9B and 15-5E) and oxygen (Sections 16-9E). 

For the activation of methane, SO4 /Zr02 was found to be active for the reaction of methane with ethylene to form C3, t-C4, 1-C5 [64] In Table 5, the product distribution is compared with that of the other solid superacid, TaFs/AEC [65] For the chlorination of methane, the selectivity of S04 /Zr02 for the formation of methyl chloride exceeds 90% with 30% of chlorine conversion at 473 K and is above 80% with 70-90% conversion at 439 K The selectivity is enhanced by adding Pt, while Fe203-Mn02-S04 /Zr02 exhibits excellent sclectivities (99-100%) at lower conversions [66] The electrophilic insertion is said to involve electron-deficient metal-coordinated chlorine at the methane C H bond... 

The idea that alkenes possessing electron-withdrawing groups are not adequate substrates for Pauson-Khand reactions has in recent years turned out not to be precise. Carretero has reported several examples involving electron-deficient alkenes 3), such as os/Tunsaturalcd ketones, esters, nitriles, sulfoxides and sulfones. In these reactions they reach good yields of PK products (4) and isolate small amounts of dienes 5, that come from a /J-climinalion competitive reaction (Scheme 5) [26,27]. 

The reactions involving electron-deficient alkenes are typified by the reaction of benzene with methyl acrylate (Atkins et al., 1977) and of anisole with acrylonitrile (Ohashi et al., 1976, 1977c). The reaction with methyl acrylate produces two stereoisomeric 1,2-cycloaddition products. It was proposed that the stereochemistry of the product is determined by the orientation of the alkene relative to benzene in the ground state complexes. There is good evidence, e.g. from studies of deuterium incorporation, that the reaction with acrylonitrile to give [127] and [128], and probably [129] involves electron transfer (Scheme 28). Anisole forms ground state complexes with maleimide... 

Iodocyclization of carbamates involving electron-deficient alkenes such as a,/l-unsaturated esters is greatly facilitated by the use of silver triflate and proceeds with excellent trans ring stereoselectivity. It is worth mentioning, however, that the resultant iodides can undergo epimerization, whose rate depends on the solvent used in the process21. 

MOLECULAR REARRANGEMENTS INVOLVING ELECTRONICALLY DEFICIENT NITROGEN ATOMS... 

The involvement of intermediates and transition states containing higher coordinate carbon has been originally proposed by Olah in both electrophilic reactions involving electron-deficient systems such as carbocations, heterocations, carbenes, nitrenes, silylenes, coordinatively unsaturated metal compounds, and so on, as well as in nucleophilic Sn2 reactions by Ingold. Whereas in electrophilic reactions, the pentacoordinate carbocationic centers are associated with eight electrons and thus can be intermediates (albeit... 

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