The Synthon Approach as a Pragmatic Tool in Elaborating Viable Synthetic Pathways

3 The Synthon Approach as a Pragmatic Tool in Elaborating Viable Synthetic Pathways 

Synthons such as 237 or 238 might appear to be non-productive as the availability of reagents corresponding to these synthons may be questionable. Nevertheless, if one takes into account the options to synthesize p-substituted aromatic compounds and their ease of conversion into ci, s -l,4-disubstituted cyclohexanes via catalytic hydrogenation), the proposed disconnections become immediately feasible. This reasoning leads to routes A and B as realistic pathways for the preparation of 236. 

Keeping in mind the availability of a Birch reaction for the partial reduction of an aromatic system, the retrosynthetic analysis of 4-rerr-butyl-3-cyclohex- 

4 Reversed Polarity Isostructnral Synthons. New Horizons in the Synthetic Application of Carbonyl Compounds 

In much the same way it is possible to introduce the aryl group (Ar) either as the Ar or Ar synthon. As we have already mentioned, hydrocarbons ArH, or organometallic reagents like ArMgBr and ArLi, can serve as the equivalents of Ar in reactions with appropriate electrophiles. For the less obvious electrophilic Ar synthon, the aryl halides can serve as suitable equivalents under appropriate conditions. Since aryl halides are usually not prone to react with regular nucleophiles, it is necessary to use cuprate reagents, R2CuLi, as nucleophiles or transition metal complexes as catalysts. 

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