Electrophiles Bound to the Polymeric Support

As well as Pd-mediated reactions, there are other processes in which electrophiles are bound to the polymeric support. These may involve Hnear chain elongation as well as cyclization. 

A common electrophile is the aldehyde moiety, which of course can be involved in many reactions with nucleophiles. The key problem is to avoid foUow-up reactions such as multiple additions or oligomerizations, which are likely to occur with many support-bound substrates. Thus, irreversible reactions are employed to achieve the desired product selectivity. In many cases these reactions require strongly basic conditions and involve Grignard reagents, or Zn, li and even In organyls [365]. N-acyliminiun ion chemistry has recently received great attention in SPOC. 

Zn alkyls, generated in situ, are very versatile reagents for alkyl-alkyl, alkyl-aryl and aryl-aryl couplings [73]. Arylzinc bromides and benzylzinc iodides may serve as more reactive substitutes for boronates or stannanes in Pd-mediated couplings. 

In the case of ortho-iodoaryltosylates, Zn insertion occurs in both the C-OTf and the C-I bond and therefore generates a reagent which may perform two aryl-aryl couplings with another aryl iodide at adjacent carbon atoms [368]. The main drawback of zinc organyls is their lability toward water and oxygen a dry box or Atmos-bagTM is recommended. 

1 Reactions Involving Crignard Reagents, Organolithium, and Organozinc Reagents 

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