Dienophiles vinylphosphonium salts

Vinylphosphonium salts are reactive as dienophiles as a result of the EWG character of the phosphonium substituent. The D-A adducts can be deprotonated to give ylides that undergo the Wittig reaction to introduce an exocyclic double bond. This sequence of reactions corresponds to a D-A reaction employing allene as the dienophile.71... 

The Diels-Alder adducts of vinylphosphonium salts may be deprotonated with base to give ylides. Subsequent reaction with a carbonyl compound introduces an exocyclic carbon-carbon double bond. This sequence of reactions thus corresponds to a Diels-Alder reaction employing a substituted allene as the dienophile. 

---

See also in sourсe #XX -- [ ]

---