Ambident substrates,

Some substrates (e.g., 1,3-dichlorobutane) can be attacked at two or more positions. We may call these ambident substrates. In the example given, there happen to be two leaving groups in the molecule, but there are two kinds of substrates that are inherently ambident (unless symmetrical). One of these, the ally lie type, has already been discussed (p. 421). The other is the epoxy (or the similar aziridine" or episulfide) substrate." ... 

The relationships between the components of the Hantzsch triangle were considered in-depth in the monograph 2 and references therein. Although the problem of reactivity of ambident substrates has been studied over many years and from different points of view, the complexity of the starting system and its numerous reaction pathways do not allow one to reliably predict the results of O-alkylation in each particular case, because it is necessary to take into account the rates of numerous reversible and irreversible processes as well as the thermodynamic factors responsible for the position of the equilibrium it is necessary to take solvent effects into consideration when estimating the thermodynamic factors. All accumulated observations are approximated by several empirical mles included in monographs 2 and 3. 

As far as substrates are concerned, while the usual 1,4-addition and 1,3-substi-tution (Sn2 ) reactions of simple unsaturated substrates have so far predominated, analogous transformations of ambident substrates with extended multiple bond systems (i.e., with two or more reactive positions) have come to attention only recently. Here, systematic investigations have shown that such 1,5-substitutions and even 1,6- and 1,8-addition reactions proceed highly regioselectively and ste-reoselectively, in particular when the substrate contains at least one triple bond besides one or more conjugated double bonds. These unusual reaction types not... 

With alkylating agents, 4-ethoxycarbonyl-2-A/-methylaminothiazines appear to be ambident substrates. It seems the thiazines cannot be directly alkylated, and alkylations are made in the anionic form (216) (65JOC2290). In dioxan, alkylation occurs at the exocyclic nitrogen, in water, alkylation concerns the endocyclic nitrogen (Scheme 89). It has been noted that there is no methylation of NH by diazomethane. 

Some substrates (e.g., 1,3-dichlorobutane) can be attacked at two or more positions. We may call these ambident substrates. In the example given, there happen to be... 

Recently, Lee et al. adopted this methodology for the cycloisomerization of aIlenyne-l,6 Hols 122. Accordingly, these ambident substrates underwent cycliza-tion smoothly into various 3-vinylfurans 123 in the presence of AgOTf catalyst (Scheme 8.49) [168]. 

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