The mechanism you described for nucleophilic ring opening is correct. You actívate the carbonyl oxygen, then you open the ring with a nucleophile. The activated carbonyl somehow has oxocarbenium like carácter.

Thank you Prof. Kaufman for your suggestion.

My aim is to know the possibility of electrophyllic ring opening of lactones. Here I have attached a mechanism to understand the question more clearly. Please provide some reference (if you have) in which ring is open by electrophile via oxocarbenium ion.

Ring opening of lactones generally occurs via nucleophilic acyl substitution, in which the nucleophile attacks the sp2 carbonyl to form a tetrahedral intermediate which then ring opens.

They can also be opened via an SN2 mechanism with nucleophilic attack at the sp3 carbon bearing an oxygen, promoted via lewis acids and soft nucleophiles, however this is less common as the carbonyl carbon is inherently more electrophilic.

If the lactone is acting as a nucleophile it does not generally react via the ring oxygen.

In acidic or basic conditions the lactone enolises and can react at the exo oxygen or at the alpha carbon. Neither of which result in ring opening.

In the absence of enolisation the electrophile reacts with the nucleophilic carbonyl oxygen. However the resulting oxocarbenium intermediate often loses a proton to form an enol and does not ring open without a nucleophile.

If enolisation were not possible then a strong electrophile could react via the carbonyl oxygen resulting in an oxocarbenium intermediate. However this is unlikely to ring open in an E1 fashion unless the resulting carbocation is stabilised as the reaction is essentially reversible and the oxocarbenium is more stable.

If you wanted to open a lactone with an electrophile then you would need to stabilise the elimination pathway and have non nucleophilic, non basic conditions or have a structure that cannot enolise (alpha tertiary carbon or alpha bridgehead).

Thanks Mr. Harris for your nice explanation. It really enhance my knowledge to understand the mechanism clearly.From your explanation it is clear that the ring opening (RO) can  proceed through route 2 and not 1 i.e., the possibility of RO via carboxenium ion is negligible in absence of a suitable nucleophile, am I right? Can you share your opinion for route 1 if we use acidic solution in water. 

When using arrows to show mechanisms they must proceed from the source of electrons. Hence the base of the arrows can never originate at a proton.

In route 1 you are effectively performing an elimination, however as I mentioned earlier. Protonation of the lactone would proceed via a non concerted E1 process generating a formal carbocation. This is a fairly high energy process and is unlikely to occur in acidic water. It would also compete with SN1 processes and electrophilic addition so that the product you desire in 1 is not achievable.

In route 2 you have acid catalysed enolisation, this would happen reversibly in your system and does not result in ring opening.

In acidic water you would get hydrolysis of the ester via the following mechanism, an acid catalysed nucleophilic acyl substitution:

@Harris_

Thanks for clarification.

The ring opening reaction by a nucleophile in lactone is due to the presence of highly electron deficient  Sp2 carbon where possibility of formation of stable transition state exists and thereafter it undergoes ring opening. It is not possible by  using electrophile because of lack of strong nucleophilic Sp2 carbon in the lactone ring.

Ring opening reaction of lactones  often follow nucleophilic pathway  is correct because   The C=O prefers nucleophilic addition. During addition   an Intermediate oxo- anion intermediate is more stabilized.

Could hydrosulfide or sulfide ions react with lactones via nucleophilic attack on the carbonyl carbon?

dear all 

please suggest i want to separate massoia lactone C-10 and C-12 by fractional distillation but i have a problem to separate them because when rise the temp.130 deg C it convert to hydroxy acid (decyn-ol)

the acid value of massoia oil lactone is 8 

please give you your opinion to prevent the hydrolysis of massoia lactone during the fractional distillation 

 great answer Teodoro S Kaufman

How LDA react with lactone?

The ring opening reaction (of lactones) often follow nucleophilic pathway and not electrophilic. This is because ring opening reaction generates electrophilic centre rather than nucleophilic centre.