Transform functional group transposition

Such a systematic review is especially useful since a knowledge of the functional group transformation is essential in retrosynthetic analysis. In the so-called transform -based strategy functional group interchanges (or interconversions FGI) or functional group transpositions (FGT) are applied to simplify a target molecule and one has to look for synthetic reactions which allow these transformations to perform. 

Another fascinating, unique property of allylic systems is their propensity for allylic rearrangement with transfer of functionality from one end of the allylic system to the other and concomitant double bond shift with or without transformation of functional groups. In the latter case (X = Y equation 1) a reaction is synthetically useful only in unsymmetrical cases for a 1,3-transposition of the functional group. 

Although both are associated with P. S. Wharton, the Wharton fragmentation is a completely different transformation than the Wharton reaction (also called the Wharton transposition, rearrangement, or reduction). For a review of the Wharton reaction, see Li, J. J. In Name Reactions for Functional Group Transformations, Li, J. J., Ed. Wiley Hoboken, New Jersey, 2007 pp 152-158. 

The transformation of an allylic alcohol to an allylic halide (equation 5) or the reverse reaction normally leads to a mixture of isomers of direct and allylic substitution products. Only when tertiary allylic alcohols are employed or a rearrangement leads to extended conjugation of double bonds does a transposition of functionality occur predominantly While a number of procedures have been developed for the conversion of allylic alcohols to halides without rearrangement, there seems to be only one reaction where a cleanly rearranged product is obtainable in a substitution of a primary or secondary allylic (and propargylic) hydroxy group to a chloride, that is by thionyl chloride in ether, probably by a cyclic SNi process. The regioselectivity is worse in other solvents and is lost in the presence of a base. In accordance with the mechanism it is a syn facial substitution, as has been demonstrated in cyclic cases (equa-... 

Reactions of Enols and Enolate Anions.—Several methods are described for transposition of an oxo-function to the adjacent site. They involve formation of a suitable a-substituted derivative (hydroxymethylene ° or benzylidene ) and subsequent steps which transform the substituent into an isolated oxo-group. Condensations leading to both the 2-hydroxymethylene- and the 2-arylidene-3-oxo-steroids are described for 3-ketones of the 5jS-series, and also of the 5j8,9j5,10a-( retro ) series.Condensations of aromatic aldehydes at C-2 in the 5 -series are unusually slow enolisation towards C-4 is preferred, but steric compression between C-4 and C-6 in 5/3-compounds severely hinders the condensation reaction at C-4, allowing reaction at C-2 via the 2-enol. Reduction of a 21-hydroxymethylene-pregnan-20-one (337) with sodium borohydride afforded the homopregnanediol (338), although reduction of enolised P-dicarbonyl compounds frequently proceeds via elimination to give enones, and thence allylic alcohols. 

---