Oxa-Michael Cascade [4+2] Annulation of Pyrazoledione-derived Morita–Baylis–Hillman (Pyro-MBH) Alcohols with Arylidene Pyarazolones: One pot Access to Dispiropyrazolone fused Tetrahydropyran

A metal-free oxa-Michael cascade [4+2] annulation has been achieved efficiently to synthesize an interesting dispiropyrazolone fused tetrahydropyran scaffold. The reaction of pyrazolonedione-based Morita−Baylis−Hillman (Pyro-MBH) alcohol with arylidene pyrazolone was explored under basic conditions to access dispiropyrazolone fused tetrahydropyran in an extremely rapid time (1-2 minutes). The method effectively explored the reactivity of Pyro-MBH alcohols as the novel oxa-Michael donors for the first time, and it did not require the corresponding reactive Pyro-MBH carbonate. This interesting complex scaffold with four chiral centres has been synthesized in very good yields in one-pot. The method is also scalable on a gram quantity, and the product has been further utilized for the post-synthetic modifications using Suzuki coupling.