A protocol for the direct functionalization of N–H/α,α,β,β-C(sp3)–H of piperidine without any metal or external oxidants is reported. This reaction is promoted by 4-(trifluoromethyl)benzoic acid via an azomethine ylide intermediate. This is a simple method for the synthesis of spirooxindoles bearing 3-substituted oxindole moieties.

AbstractSpirooxindoles bearing a 1-azabicyclo[5.3.0]decane moiety were synthesized in one step via direct functionalization of the azepane without a transition metal or oxidants. This is an efficient process for the synthesis of fused 7/5-heterobicyclic systems in one step. Furthermore, cycloaddition of the in-situ-generated azomethine ylide only proceeded for alkenyl sulfone dipolarophiles.

The [4+3] annulation reaction of crotonate-derived sulfur ylides with thioaurones has, for the first time, been reported using NaH as the base. A diverse array of 2,5-dihydrobenzo[4,5]thieno[3,2-b]oxepines is obtained in good to excellent yields. The proposed mechanism is investigated and supported by DFT calculations.

A DABCO-catalyzed domino reaction between methyleneoxindoles and allenoates which enables the direct synthesis of spirooxindoles is reported. This is the first example of a non-substituted allenoate to act as a four-carbon synthon in a tertiary amine-catalyzed reaction.

We first reported an example of diverse synthesis of pyrano[2,3-b]indol and dihydropyrano[2,3-b]indol from the same starting materials. In these domino reactions, we can control the reaction conditions to give three new products: pyrano[2,3-b]indol, dihydropyrano[2,3-b]indol with E or Z exocyclic double bond. Using DABCO as catalyst in THF, dihydropyrano[2,3-b]indol with E exocyclic double bond and pyrano[2,3-b]indol were obtained at room temperature and 65 °C, respectively. In contrast, when DMAP was selected as catalyst, dihydropyrano[2,3-b]indol with Z exocyclic double bond was formed in toluene at 80 °C.

A DABCO-catalyzed domino reaction between methyleneoxindoles and allenoates which enables the direct synthesis of spirooxindoles is reported. This is the first example of a non-substituted allenoate to act as a four-carbon synthon in a tertiary amine-catalyzed reaction.

A protocol for the direct functionalization of N–H/α,α,β,β-C(sp3)–H of piperidine without any metal or external oxidants is reported. This reaction is promoted by 4-(trifluoromethyl)benzoic acid via an azomethine ylide intermediate. This is a simple method for the synthesis of spirooxindoles bearing 3-substituted oxindole moieties.