Which of the following is an ideal Click reaction
1) Cyannohydrin formation from acetaldehyde
2) Diels Alder cyclo addition
3) Attack of triplet carbene on cis-2-butene
4) Ziegler Natta polymerisation
Click Chemistry: is a chemical philosophy introduced by Karl Barry Sharpless , the Noble Prize Winner in Chemistry for2001.It describes chemistry tailored to generate substances quickly and reliably by joining small units together. "Click" is meant to signify that the joining molecuar pieces is as easy as clicking together two pieces of bucle. This inspired by the fact that nature also generates substances by joining together small modular units.
Following is the list of 10 Click Commendments.
The process must be:
2) Wide in scope
3) Give high chemical yield of product
4) Generate only inoffensive by products, if any.
The process Must have:
6) Simple reaction Conditions
7) Readily available starting materials
8) No solvent or benign solvent (prefareably water)
9) Easy product isolation by distillation or crystllisation (no chromatography)
10) Large thermodynamic diving force > 84kJ
It has been awhile since my undergraduate Chemistry days, but from what I recall, some of the criterion for "Click Chemistry" are rather subjective.
In short, I would venture that the Diels-Alder cyclo addition is the most ideal Click rxn. My analysis:
1) Cyanohydrin formation from an aldehyde is not stereospecific because the cyanide ion can attack from the front face or back face of the cabonyl group, with each yielding a different product (enantiomers). I believe this yield will be 50/50 - a raceimic mixture.
3) A triplet carbene will not provide for a concerted addition because two of its orbitals are occupied by lone electrons, thus making it a poor electrophile. As a result, there will be a intermediaries in the form of a biradical. Also, the carbons that were previously double bonded will now only have a sigma bond allowing rotation, which will result in the loss of steriochemistry.
4) Ziegler Natta polymerization involves a catalyst that is not readibly availabe, nor is it very easy to make. In fact, IIRC it isn't even stable in air and must be prepared under an inert atmosphere.
By process of elimination, this leaves the Diels-Alder rxn, although Diels-Alder doesn't necessarily conform to #10 since typically it requires very little energy. I guess that is where the subjectivity comes in.
This is my best guess, and I would probably be willing to put my BS in Chemistry on the line for it. However, I would recommend that you hop on over to Chemical Forums: Chemistry Help, Chemistry Forums and Chemistry Fun - Index and post in the 'Undergraduate Chemistry Forum' or the 'Organic Chemistry Forum'.
Please let me know if any of the above was incorrect - I'm also not a practicing chemist.