This first retrosynthetic step involves the intramolecular
version of an
esterifcation reaction. The generalized forward reaction is simply ROH +
R'COOH (with acid or basic catalysis), where both functional groups are
present in the same molecule.
Analyzing the next target, A, one recognizes the alpha beta
unsaturated carbonyl pattern, which is suggestive of an aldol
In the forward sense, this reaction would be best carried out by using the
enolate derived from C, with subsequent hydrolysis and decarboxylation, as
Fragment B contains a 1,3 oxygenation pattern -- more sepcifically
hydroxy aldehyde, a recognizable aldol product.
In the evaluation of the forward step, we again see that while this is a
mixed aldol reaction, there is only one position with an enolizable
and the reaction is deemed feasible.