91Ó°ÊÓ

Retrosynthesis is defined as a logical approach for designing an organic synthesis which involves a breaking down of target molecule in to available or given starting material by the imaginary breaking of bonds.

(a) 1, 3 or β-hydroxycarbonyl compounds have a 1,3-relationship between functionalized carbons. This compound can be disconnected at one C-C bond between the functional groups to give enolate of one carbonyl compound reacting with either acid derivatives or acid chlorides to give the desired product as shown below:

(b)In compound (b) disconnection of a 1,4-dioxgenated compound shows it can be synthesized by nucleophilic attack of a negatively charged α-carbon (an enolate ion) on a compound with a positively charged α-carbon. An α-brominated carbonyl compound is a synthetic equivalent for the positively charged α-carbon, and an enamine is the synthetic equivalent for the negatively charged α-carbon. Because esters cannot form enamines. The following disconnection approach is shown below:

(c) In compound (c), the simplest way to find the starting material is to carry out disconnection by the reverse ozonolysis, it also shows disconnection of a 1,4-dioxgenated compound and can be synthesized by nucleophilic attack of a negatively charged α-carbon (an enolate ion) on a compound with a positively charged α-carbon as in (b) synthesis. The following disconnection approach is shown below:

(d) In compound (d), the disconnection of a 1,5-dioxgenated compound shows it can be synthesized by nucleophilic attack of a negatively charged α-carbon on a carbonyl compound with a positively charged β-carbon. An α,β-unsaturated carbonyl compound is the synthetic equivalent of a compound with a positively charged β-carbon. And we saw that an enamine is the synthetic equivalent for the negatively charged α-carbon.

The following disconnection approach is shown below:

(e) The simplest way to find the starting material is to carry out disconnection by the reverse ozonolysis and Diels-Alder reaction.