Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. In Chemistry, chemical synthesis is purposeful execution of Chemical reactions in order to get a product, or several products An organic compound is any member of a large class of Chemical compounds whose Molecules contain Carbon. Organic reactions are Chemical reactions involving Organic compounds The basic Organic chemistry reaction types are Addition reactions Elimination Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has developed into one of the most important aspects of organic chemistry. Organic chemistry is a discipline within Chemistry which involves the scientific study of the structure properties composition reactions, and preparation Inorganic chemistry is the branch of Chemistry concerned with the properties and behavior of Inorganic compounds This field covers all Chemical compounds An organic compound is any member of a large class of Chemical compounds whose Molecules contain Carbon. Organic chemistry is a discipline within Chemistry which involves the scientific study of the structure properties composition reactions, and preparation There are two main areas of research fields within the general area of organic synthesis: total synthesis and methodology. In principle a total synthesis is the complete Chemical synthesis of complex organic Molecules from simpler pieces usually without the aid of biological Methodology (also called manner) is defined as "the analysis of the principles of methods rules and postulates employed by a discipline"

Contents 1 Total synthesis 2 Methodology 3 Asymmetric synthesis 4 Synthesis design 5 See also 6 References 7 External links

Total synthesis

Main article: Total synthesis

A total synthesis^[1] is the complete chemical synthesis of complex organic molecules from simple, commercially available (petrochemical) or natural precursors. In principle a total synthesis is the complete Chemical synthesis of complex organic Molecules from simpler pieces usually without the aid of biological In Chemistry, chemical synthesis is purposeful execution of Chemical reactions in order to get a product, or several products An organic compound is any member of a large class of Chemical compounds whose Molecules contain Carbon. In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by Petrochemicals are chemical products made from raw materials of Petroleum or other Hydrocarbon origin Nature, in the broadest sense is equivalent to the natural world, physical universe, material world or material universe. 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. In Chemistry a convergent synthesis is a strategy that aims to improve the efficiency of multi-step Chemical synthesis. 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^[2]. Robert Burns Woodward ( April 10 1917 &ndash July 8 1979) was an American organic chemist. The Nobel Prize in Chemistry (Nobelpriset i kemi is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of Chemistry. Strychnine (ˈstrɪkniːn (British US /-naɪn/ or /-nɪn/ (US Some modern examples include Wender's, Holton's, Nicolaou's and Danishefsky's synthesis of Taxol. The Holton Taxol total synthesis, published by Robert A Holton and his group at Florida State University in 1994 was the first Total synthesis of The Nicolaou taxol total synthesis, published by K C Nicolaou and his group in 1994 concerns the Total synthesis of Taxol. The Danishefsky Taxol total synthesis in Organic chemistry is an important third Taxol synthesis published by the group of Samuel Danishefsky in 1996 two

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^[3]. A chemical reaction is a process that always results in the interconversion of Chemical substances The substance or substances initially involved in a chemical reaction are called A reagent or reactant is a substance or compound consumed during a Chemical reaction. 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 yields and to be reliable for a broad range of substrates. Methodology research usually involves three main stages- discovery, optimisation, and studies of scope and limitations. The discovery requires extensive knowledge of and experience with chemical reactivities of appropriate reagents. 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

Main article: Chiral synthesis

Many complex natural products occur as one pure enantiomer. Asymmetric synthesis, also called chiral synthesis, enantioselective synthesis or stereoselective synthesis, is Organic synthesis which In Chemistry, an enantiomer ( from the Greek ἐνάντιος opposite and μέρος part or portion is one of two Stereoisomers that are nonsuperimposable Traditionally, however, a total synthesis could only make a complex molecule as a racemic mixture, i. In Chemistry, a racemic mixture, or racemate, is one that has equal amounts of left- and right-handed enantiomers of a chiral e. , as an equal mixture of both possible enantiomer forms. In Chemistry, an enantiomer ( from the Greek ἐνάντιος opposite and μέρος part or portion is one of two Stereoisomers that are nonsuperimposable The racemic mixture might then be separated via chiral resolution. Chiral resolution in Stereochemistry is a process for the separation of Racemic compounds into their Enantiomers It is an important tool in the production

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. Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst In kinetic resolution two Enantiomers show different Reaction rates in a Chemical reaction thereby creating an excess of the less reactive enantiomer. 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. The Sharpless epoxidation reaction is an enantioselective Chemical reaction to prepare 23-epoxyalcohols from primary and secondary allylic alcohols This Karl Barry Sharpless (born April 28, 1941) is an American Chemist known for his work on Stereoselective reactions. Hydrogenation is the Chemical reaction that results in addition of Hydrogen (H2 William S Knowles (born June 1, 1917) is an American Chemist. (born September 3, 1938) is a Japanese chemist He won the Nobel Prize in Chemistry in 2001 The Nobel Prize in Chemistry (Nobelpriset i kemi is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of Chemistry. 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. Robert Burns Woodward ( April 10 1917 &ndash July 8 1979) was an American organic chemist. 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 retrosynthetic analysis, for which he won the Nobel Prize for Chemistry in 1990. Elias James Corey (born July 12, 1928) is an American organic chemist. Retrosynthetic analysis is a technique for solving problems in the planning of organic syntheses. The Nobel Prize in Chemistry (Nobelpriset i kemi is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of Chemistry. In this approach, the research is planned backwards from the product, using standard rules^[4]. 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. Computational chemistry is a branch of Chemistry that uses computers to assist in solving chemical problems Hendrickson, who developed a computer program for designing a synthesis based on sequences of generic "half-reactions". Computer-aided methods have recently been reviewed. ^[5]

See also

• Organic Syntheses, a publication which gives detailed peer-tested laboratory procedures. Organic Syntheses is a Scientific journal that since 1921 has provided the Chemistry community with annual collections of detailed and checked procedures
• Methods in Organic Synthesis, a journal

References

External links

• http://www.webreactions.net/search.html
• http://www.organic-chemistry.org/synthesis/
• Natural product syntheses

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