In chemistry

Chemistry

Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

 a convergent synthesis is a strategy that aims to improve the efficiency of multi-step chemical synthesis

Chemical synthesis

In chemistry, chemical synthesis is purposeful execution of chemical reactions to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions...

, most often in organic synthesis

Organic synthesis

Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

. In linear synthesis the overall yield quickly drops with each reaction step:

A → B → C → D

Suppose the yield is 50% for each reaction, the overall yield of D is only 12.5% from A.

In a convergent synthesis

A → B (50%)

C → D (50%)

B + D → E (25%)

the overall yield of E (25%) looks much better. Convergent synthesis is applied in the synthesis of complex molecules (see total synthesis

Total synthesis

In organic chemistry, a total synthesis is, in principle, the complete chemical synthesis of complex organic molecules from simpler pieces, usually without the aid of biological processes. In practice, these simpler pieces are commercially available in bulk and semi-bulk quantities, and are often...

) and involve fragment coupling and independent synthesis.

Examples:

• Convergent synthesis is encountered in dendrimer
  Dendrimer
  Dendrimers are repetitively branched molecules. The name comes from the Greek word "δένδρον" , which translates to "tree". Synonymous terms for dendrimer include arborols and cascade molecules. However, dendrimer is currently the internationally accepted term. A dendrimer is typically symmetric...
  
   synthesis where branches (with the number of generations preset) are connected to the central core
• Proteins of up to 300 amino acid
  Amino acid
  Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
  
  s are produced by a convergent approach using chemical ligation
  Chemical ligation
  Chemical ligation is a set of techniques used for creating long peptide or protein chains. It is the second step of a convergent approach. First, smaller peptides containing 30-50 amino acids are prepared by conventional chemical peptide synthesis. Then, they are completely deprotected...
  
  .
• An example of its use in total synthesis
  Total synthesis
  In organic chemistry, a total synthesis is, in principle, the complete chemical synthesis of complex organic molecules from simpler pieces, usually without the aid of biological processes. In practice, these simpler pieces are commercially available in bulk and semi-bulk quantities, and are often...
  
   is the final step (photochemical [2+2]cycloaddition
  Cycloaddition
  A cycloaddition is a pericyclic chemical reaction, in which "two or more unsaturated molecules combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity." The resulting reaction is a cyclization reaction.Cycloadditions are usually described by the...
  
  ) towards the compound Biyouyanagin A :