Previous - 1.1 General approach (PLANNING)
1.2 Which Reaction? (PDF version)
1. Write out possibilities (from memory)
2. Carry out Scifinder search
3. Refine : find 3-5 options which repeat regulary (i.e have most hits).
4. Filter options above according to the following criteria:
- COST
Price of scale-up – too expensive for high throughput of material?
Note: depends where in sequence reagent occurs: end vs start
- TOXICITY
Avoid heavy metals: common villains: Cr/Hg/Sn/Pb/Se/
Toxic organic products HMPA
- EASE OF CARRYING OUT
Things to watch out for
Special reagents required? commercially available? Requires synthesis?
Requires buying in reagent. (vs reagents in stock)
Anhydrous conditions required (vs wet/non anhydrous conditions)
Special handling conditions e.g glovebox.
High boiling point solvent required? DMF/DMSO/DMPU etc
Special apparatus? High pressure vessel/gas cylinder etc
- FUTURISTIC “COOL FACTOR”
Some reactions look better in publications e.g those with Pd/Ru/organocatalysis/obscure reagents than classic tried and tested reagents.
Cross metathesis vs wittig reaction
- FUNCTIONAL GROUP COMPATIBILITY
Ensure the reactions conditions chosen are compatible with ALL the functional groups present in your molecule:
e.g Jones reagent (contains H2SO4) would not be compatible with acid sensitive groups such as acetals for example.
- INTUITION
Sometimes choice depends on intution as to what seems the best option – subtle combinations of the above factors which is difficult to express in words.