one group disconnection
Toeget molecule
OH
Me
fur
С C
1
11e
'CN
Branch point
19-6
Answers
Answer:
1. Synthon or Disconnection or Retrosynthesis Approach in Organic Synthesis Presented by: Ms. Sarika Mohite B.Pharm , M.Pharm IIIrd Semester Guided by: Dr . Amit G. Nerkar, Associate Professor in Medicinal Chemistry, Sinhgad Technical Education Society’sSmt. Kashibai Navale College of Pharmacy, Kondhwa(Bk), Pune-48, Maharashtra, India
2. An analytical approach in organic synthesis in which the target molecule is brokeninto fragments through a series of logical disconnection to get the best possible &likely starting materials ( Synthon) An analytical operation that breaks a bond & converts a molecule into possible starting materials It is exactly the reverse of chemical synthesis .Therefore also called Reterosynthesis TerminologiesDisconnection – An operation involving breaking of bonds between atomsSynthon – An idealized fragment usually an ion or radical obtained by disconnectionReagent – Actual comp (chemicals) used in practice for a synthesis e.g.- Synthon-Me⁺ Reagent-Me2SO4
3. FGI or FGE – Functional group interconversion or functional group equivalence usually written on double arrow This means substitution of functional group by another one equivalent to it. e.g.- -COOH FGI -CN -NH2 -NO2 -Cl -OH Basic rule Disconnection of a bond should be such that stable fragment ion are obtained e.g. two mode of disconnection A&B A - + O 2N C C R O 2N C C R B + - O 2N C C RA will be preferred as carbocations are stabilized by electron donor gr. R,OR ,etc,While carbinions are stabilized by electron withdrawing gr. NO2,CN,COOR etc.
4. Number of fragments generated through a disconnection should be as minimum aspossible O O O O + - C H 2C R R R R + O R O 2 O halo R OC 2 H 5 R 1 3 OH O O 5 4 O R R O O O O + C R R R - H2C R O O 2 1 R R
5. Always a C-hetero atom (O,S,N) bond is broken ,with the electron pair beingtransferred to the heteroatom (as heteroatom are more electro negative than Cthey can accommodate the electron pair ) + - C N C N .. .. C Cl HN ..
6. Some time a disconnection doesn’t generate sufficient stabilised fragments butsuch fragment can be obtained using FGI or introducing additional electronwithdrawing & removing them . a CH2 + NH3 R NH2 R b R X + - R CH2 NH2 (not sufficiently stabilised) Cl - CH2NO2 ( introduction of electrowithdrawing groups R
7. The –ve & + ve fragments generated by disconnection are replaced by recognizable &Meaningful chemical entities. + R-CH2-X(alkyl halide) R-CH2 R-CH2-OH(alcohol) ( vely charged alkyl) R-CH2OC2H5(ether) + R-C=O ( vely charged acyl) R-CO-X(acylhalid) R-CO-OH(acid) R-CO-OC2H5(ester) R-CO-O-CO-R(anhydride) - O2N-CH-R O2N-CH2-R - R-O R-O-H - R-NH RNH2 - vely charged fragments are considered equivalent to their protonated species .