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An approach for designing organic synthesis which involves breaking down of target molecule into available starting material by imaginary breaking of bonds (disconnection) and/or by functional group interconversion is known as disconnection approach or retrosynthesis or synthesis backward.
The C-X disconnection approach is mainly applicable to a carbon chain attached to any of the heteroatoms like O, N, or S. Here, a bond joins the heteroatom (X) to the rest of the molecule like a C-O, C-N, or C-S group. This point is good point to initiate a disconnection. This is called a ‘One-group’ C-X disconnection as one would need to identify only one functional group like ester, ether, amide etc. to make the disconnection.
How to choose a disconnection?
These are the few general strategy which are important points introduced which apply to the whole of synthetic design rather than one particular area. The main choice is between the various disconnection, even such a simple disconnection as the following alcohol can be disconnected.
We want to get back to simple starting materials and we shall do if we disconnect the bond which are:
Towards the middle of the molecule thereby breaking into two reasonably equal halves rather than chopping off one or two carbon atoms from the end and,
At a branch as this is more likely to give straight chain fragments and these are more likely to be available.
Disconnections very often take place immediately adjacent to, or very close to functional groups in the target molecule. This is pretty much inevitable, given that functionality almost invariably arises from the forward reaction.
A simple example is the weedkiller propanil used on rice fields. Amide disconnection gives amine obviously made from o-dichlorobenzene by nitration and reduction. All positions around the ring in o-dichlorobenzene are about the same electronically but steric hindrance will lead to dichloronitrobenzene being the major product
This compound was needed for some research into the mechanisms of rearrangements. We can disconnect on either side of the ether oxygen atom, but (b) is much better because (a) does not correspond to a reliable reaction: it might be hard to control selective alkylation of the primary hydroxyl group in the presence of the secondary one.
The disconnections we have made so far have all been of C–O, C–N, or C–S bonds, but, of course, the most important reactions in organic synthesis are those that form C–C bonds. We can analyze C–C disconnections in much the same way as we’ve analyzed C–X disconnections.
The Zeneca drug propranolol is a beta-blocker that reduces blood pressure and is one of the top drugs worldwide. It has two 1,2-relationships in its structure but it is best to disconnect the more reactive amine group first.
Arildone is a drug that prevents polio and herpes simplex viruses from ‘unwrapping’ their DNA, and renders them harmless.
An approach for designing organic synthesis which involves breaking down of target molecule into available starting material by imaginary breaking of bonds (disconnection) and/or by functional group interconversion is known as disconnection approach or retrosynthesis or synthesis backward.
The C-X disconnection approach is mainly applicable to a carbon chain attached to any of the heteroatoms like O, N, or S. Here, a bond joins the heteroatom (X) to the rest of the molecule like a C-O, C-N, or C-S group. This point is good point to initiate a disconnection. This is called a ‘One-group’ C-X disconnection as one would need to identify only one functional group like ester, ether, amide etc. to make the disconnection.
How to choose a disconnection?
These are the few general strategy which are important points introduced which apply to the whole of synthetic design rather than one particular area. The main choice is between the various disconnection, even such a simple disconnection as the following alcohol can be disconnected.
We want to get back to simple starting materials and we shall do if we disconnect the bond which are:
Towards the middle of the molecule thereby breaking into two reasonably equal halves rather than chopping off one or two carbon atoms from the end and,
At a branch as this is more likely to give straight chain fragments and these are more likely to be available.
Disconnections very often take place immediately adjacent to, or very close to functional groups in the target molecule. This is pretty much inevitable, given that functionality almost invariably arises from the forward reaction.
A simple example is the weedkiller propanil used on rice fields. Amide disconnection gives amine obviously made from o-dichlorobenzene by nitration and reduction. All positions around the ring in o-dichlorobenzene are about the same electronically but steric hindrance will lead to dichloronitrobenzene being the major product
This compound was needed for some research into the mechanisms of rearrangements. We can disconnect on either side of the ether oxygen atom, but (b) is much better because (a) does not correspond to a reliable reaction: it might be hard to control selective alkylation of the primary hydroxyl group in the presence of the secondary one.
The disconnections we have made so far have all been of C–O, C–N, or C–S bonds, but, of course, the most important reactions in organic synthesis are those that form C–C bonds. We can analyze C–C disconnections in much the same way as we’ve analyzed C–X disconnections.
The Zeneca drug propranolol is a beta-blocker that reduces blood pressure and is one of the top drugs worldwide. It has two 1,2-relationships in its structure but it is best to disconnect the more reactive amine group first.
Arildone is a drug that prevents polio and herpes simplex viruses from ‘unwrapping’ their DNA, and renders them harmless.
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