La '''sintesi organica''' è la costruzione di molecole organiche attraverso processi chimici. Le [[molecola|molecole]] [[Chimica organica|organiche]] hanno spesso un grado di complessità superiore ai composti [[chimica inorganica|inorganici]], perciò la sintesi di composti organici è
venuta a costituire uno dei più importanti aspetti della [[chimica]] organica.
'''Organic synthesis''' is the construction of organic molecules via chemical processes. [[Organic_chemistry|Organic]] molecules can often contain a higher level of complexity compared to purely [[Inorganic_chemistry|inorganic]] compounds, so the synthesis of [[organic compound]]s has developed into one of the most important aspects of [[organic chemistry]]. There are two main areas of research fields within the general area of organic synthesis- [[Total_synthesis|''total synthesis'']] and ''methodology''.
== Total synthesis ==
A [[total synthesis]]<sup></sup> is the complete [[chemical synthesis]] of complex [[Organic_compound|organic]] [[molecule]]s from simple, commercially available ([[petrochemical]]) or [[natural]] precursors. In a ''linear'' synthesis there is a series of steps which are performed one after another until the molecule is made- this is often adequate for a simple structure. The chemical compounds made in each step are usually referred to as ''synthetic intermediates''. For more complex molecules, a [[convergent synthesis]] is often preferred. This is where several "pieces" (key intermediates) of the final product are synthesized separately, then coupled together, often near the end of the synthesis.
The "father" of modern organic synthesis is regarded as [[Robert Burns Woodward]], who received the 1965 [[Nobel Prize for Chemistry]] for several brilliant examples of total synthesis such as his 1954 synthesis of [[strychnine]]<sup></sup>. One of the most active research groups today is that of [[Kyriacos Costa Nicolaou]] of the [[Scripps Research Institute]].
== Methodology ==
Each step of a synthesis involves a [[chemical reaction]], and reagents and conditions for each of these reactions need to be designed to give a good yield and a pure product, with as little work as possible<sup></sup>. A method may already exist in the literature for making one of the early synthetic intermediates, and this method will usually be used rather than "trying to reinvent the wheel". However most intermediates are compounds that have never been made before, and these will normally be made using general methods developed by methodology researchers. To be useful, these methods need to give high [[yield]]s and to be reliable for a broad range of [[substrate]]s. Methodology research usually involves three main stages- ''discovery'', ''optimisation'', and studies of ''scope and limitations''. The ''discovery'' may be due to [[serendipity]], or may be from a flash of insight. ''Optimisation'' is where one or two starting compounds are tested in the reaction under a wide variety of conditions of temperature, solvent, reaction time, etc., until the optimum conditions for product yield and purity are found. Then the researcher tries to extend the method to a broad range of different starting materials, to find the scope and limitations. Some larger research groups may then perform a total synthesis (see above) to showcase the new methodology and demonstrate its value in a real application.
== Asymmetric synthesis ==
Many complex natural products occur as one pure [[enantiomer]]. Traditionally, however, a total synthesis could not easily make only a complex molecules as a [[Racemate|racemic]] mixture, i.e., as an equal mixture of both possible [[enantiomer]] forms. The racemic mixture might then be separated via [[chiral resolution]].
In the latter half of the twentieth century, chemists began to develop methods of asymmetric [[catalysis]] and [[kinetic resolution]] whereby reactions could be directed to produce only one enantiomer rather than a racemic mixture. Early examples include [[Sharpless epoxidation]] ([[K. Barry Sharpless]]) and asymmetric [[hydrogenation]] ([[William S. Knowles]] and [[Ryoji Noyori]]), and these workers went on to share the [[Nobel Prize in Chemistry]] in 2001 for their discoveries. Such reactions gave chemists a much wider choice of enantiomerically pure molecules to start from, where previously only natural starting materials could be used. Using techniques pioneered by [[Robert B. Woodward]] and new developments in synthetic methodology, chemists became more able to take simple molecules through to more complex molecules without unwanted racemisation, by understanding [[stereocontrol]]. This allowed the final target molecule to be synthesised as one pure enantiomer without any resolution being necessary. Such techniques are referred to as '''asymmetric synthesis'''.
== Synthesis design ==
[[Elias James Corey]] brought a more formal approach to synthesis design, based on [[Retrosynthesis|retrosynthetic analysis]], for which he won the [[Nobel Prize for Chemistry]] in 1990. In this approach, the research is planned backwards from the product, using standard rules<sup></sup>. The steps are shown using retrosynthetic arrows (drawn as =>), which in effect means "is made from". Other workers in this area include one of the pioneers of [[computational chemistry]], [[James B. Hendrickson]], who developed a computer program for designing a synthesis based on sequences of generic "half-reactions". Computer-aided methods have recently been reviewed.<sup></sup>
K. C. Nicolaou, E. J. Sorensen, ''Classics in Total Synthesis'', VCH, New York, 1996.▼
== See also ==
R. B. Woodward, M. P. Cava, W. D. Ollis, A. Hunger, H. U. Daeniker, K. Schenker, ''[[Journal of the American Chemical Society]]'' '''76''', 4749 (1954).▼
[[Organic Syntheses]], a publication which gives detailed peer-tested laboratory procedures.
J. March, D. Smith, ''Advanced Organic Chemistry''
, 5th ed.
, Wiley, New York, 2001.▼
E. J. Corey, X-M. Cheng, ''The Logic of Chemical Synthesis'', Wiley, New York, 1995.▼
== References ==
# K. C. Nicolaou, E. J. Sorensen, ''Classics in Total Synthesis'', VCH, New York, 1996.
# R. B. Woodward, M. P. Cava, W. D. Ollis, A. Hunger, H. U. Daeniker, K. Schenker, ''[[Journal of the American Chemical Society]]'' '''76''', 4749 (1954).
# J. March, D. Smith, ''Advanced Organic Chemistry'', 5th ed., Wiley, New York, 2001.
# E. J. Corey, X-M. Cheng, ''The Logic of Chemical Synthesis'', Wiley, New York, 1995.
# Matthew H. Todd, ''Computer-aided organic synthesis'', ''Chemical Society Reviews'', '''34''', 247-266 (2005). A very readable review available [http://pubs.rsc.org/ej/CS/2005/b104620a.pdf online (Subscription required)].