Correct option is D
Wittig Reaction
The Wittig reaction is a connective alkene-forming reaction.
Phosphorus atoms, especially those that are positively charged or that carry electronegative substituents, can increase the acidity of protons adjacent to them on the carbon skeleton. Phosphonium salts (made in a manner analogous to the formation of ammonium salts from amines, in other words, by reaction of an alkyl halide with a phosphine) can therefore be deprotonated by a moderately strong base to give a species known as an ylid, carrying (formally) a positive and a negative charge on adjacent atoms. Ylids can alternatively be represented as doubly bonded species, called phosphoranes.
Ylids can be isolated, but are usually used in reactions immediately they are formed. They are nucleophilic species that will attack the carbonyl groups of aldehydes or ketones, generating the four-membered ring oxaphosphetane intermediates. Oxaphosphetanes are unstable: they undergo elimination to give an alkene (65% yield for this particular example) with a phosphine oxide as a byproduct. The phosphorus–oxygen double bond is extremely strong and it is this that drives the whole reaction forward.
The Cope rearrangement is an extensively studied organic reaction involving the [3,3]-sigmatropic rearrangement of 1,5-dienes. Two π-bonds are breaking while two new π-bonds are forming, and simultaneously the σ-bond is breaking while a new σ-bond is forming. In organic chemistry, a sigmatropic reaction is a pericyclic reaction wherein the net result is one sigma bond (σ-bond) is changed to another σ-bond in an intramolecular reaction. In this type of rearrangement reaction, a substituent moves from one part of a π-system to another part with simultaneous rearrangement of the π-system. Sigmatropic rearrangements are concisely described by an order term [i,j], which is defined as the migration of a σ-bond adjacent to one or more π systems to a new position (i−1) and (j−1) atoms removed from the original location of the σ-bond.
The Claisen rearrangement is a powerful carbon–carbon bond-forming chemical reaction. The heating of an allyl vinyl ether will initiate a [3,3]-sigmatropic rearrangement to give a γ,δ-unsaturated carbonyl, driven by exergonically favored carbonyl CO bond formation.
Transesterification is the process of exchanging the organic functional group R″ of an ester with the organic group R' of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst. Strong acids catalyze the reaction by donating a proton to the carbonyl group, thus making it a more potent electrophile. Bases catalyze the reaction by removing a proton from the alcohol, thus making it more nucleophilic.
