Naphthalene competitive alkylation

Further studies by Brown and coworkers lent additional support to this mechanism and the absence of a free alkyl cation. Olah and coworkers have applied the concept of competitive alkylation to the case of naphthalene in order to study both positional and substrate selectivities, and to clarify the nature of kinetically versus thermodynamically controlled product composition. They explained the observed results by suggesting that a ir-complex, such as (1), was the intermediate involved when highly electrophilic catalysts or strongly basic aromatics were employed, and a o-complex (as proposed earlier by Brown) was involved in reactions with weakly electrophilic catalysts or less basic aromatics. 

Olah and Olah reported a competitive alkylation mechanism study of naphthalene in 1976 and postulated that the positional and substrate selectivities of napthalene F-C alkylation shed insight on the kinetically... 

Grignard reagent.80 Competition by nucleophilic aromatic substitution was not observed unless the only active position(s) was (were) substituted with a leaving group, as in the reaction of l-methoxy-2-nitro-naphthalene which gave 1 -alkyl-2-nitronaphthalenes in 73-95% yields.81 The use of Me3SiCH2MgCl (Peterson reagent) provides an entry to nitro-substituted benzyl anion intermediates, as shown in the example of Scheme 9.82... 

We also note that when ion radical reactivity is slowed, ex-ciplex chemistry (which is completely different) becomes competitive. Thus, in the reaction with acenaphthene several products corresponding to the expected pattern for benzylation (see Scheme 12) are formed. However, here product II (which does not arise from secondary photocycloaddition from one of the previously mentioned products) Is also produced. This can be explained by an initial [2-f2] photocycloaddition between the two naphthalene rings which precedes alkylation (Scheme 3). Thus, when the donor is a naphthalene rather than a benzene derivative, the twofold effect of the diminished acidity of the benzylic position and of the increased 7i-donor-acceptor interaction makes the exciplex path sufficiently important to compete with the ion pair chemistry. Going further this way, i.e. toward more positive AG , cycloaddition via exciplex completely dominates, as indicated in Section 2. 

The kinetic competition between C -C and C -C cyclization of enyne-allene 3.535 is determined by the nature of substituents in the acetylene branch. Hydrogen or n-alkyl substituents lead to the domination of the C -C reaction to form naphthalene derivative 3.538, while substituents stabilizing the radical and bulky substituents at QJ favor the C -C process and the formation of cyclised compounds 3.539 and 3.540 (the formal product of the Diels-Alder reaction with = Ph) (Scheme 3.35) [269aj. 

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