Correct option is C
The Prins reaction is an organic reaction consisting of an electrophilic addition of an aldehyde or ketone to an alkene or alkyne followed by capture of a nucleophile or elimination of an H+ ion. The outcome of the reaction depends on reaction conditions. With water and a protic acid such as sulfuric acid as the reaction medium and formaldehyde the reaction product is a 1,3-diol. When water is absent, the cationic intermediate loses a proton to give an allylic alcohol. With an excess of formaldehyde and a low reaction temperature the reaction product is a dioxane. When water is replaced by acetic acid the corresponding esters are formed.
The reaction mechanism for this reaction is depicted in scheme 5. The carbonyl reactant (2) is protonated by a protic acid and for the resulting oxonium ion 3 two resonance structures can be drawn. This electrophile engages in an electrophilic addition with the alkene to the carbocationic intermediate 4. Exactly how much positive charge is present on the secondary carbon atom in this intermediate should be determined for each reaction set. Evidence exists for neighbouring group participation of the hydroxyl oxygen or its neighboring carbon atom. When the overall reaction has a high degree of concertedness, the charge built-up will be modest.
The three reaction modes open to this oxocarbenium intermediate are:
in blue: capture of the carbocation by water or any suitable nucleophile through 5 to the 1,3-adduct 6.
in black: proton abstraction in an elimination reaction to unsaturated compound 7. When the alkene carries a methylene group, elimination and addition can be concerted with transfer of an allyl proton to the carbonyl group which in effect is an ene reaction in scheme 6.
in green: capture of the carbocation by additional carbonyl reactant. In this mode the positive charge is dispersed over oxygen and carbon in the resonance structures 8a and 8b. Ring closure leads through intermediate 9 to the dioxane 10.
in gray: only in specific reactions and when the carbocation is very stable the reaction takes a shortcut to the oxetane 12. The photochemical Paternò–Büchi reaction between alkenes and aldehydes to oxetanes is more straightforward.
In the given question, SnCl4 (Lewis acid) coordinates with the lone pair of oxygen.
The positive charge on oxygen coordinated to Lewis acid will undergo neutralization by bond breaking and formation of oxonium ion.
The next step is the Prins reaction. The last step is the Pinacol rearrangement.
The pinacol–pinacolone rearrangement is a method for converting a 1,2-diol to a carbonyl compound in organic chemistry. The 1,2-rearrangement takes place under acidic conditions. The name of the rearrangement reaction comes from the rearrangement of pinacol to pinacolone.
