The N-heterocyclic carbene catalyzed (NHC-catalyzed) generation of unsubstituted dienolate (butadienolate) and subsequent [4+2] annulation reactions with isatins afford chiral spirocyclic oxindolodihydropyranones in moderate to good yields with moderate to good enantioselectivities.

Bifunctional N-heterocyclic carbenes with a free hydroxy group are demonstrated as efficient catalysts for the [3+4] annulation of enals with aurones to give the corresponding benzofuran-fused ε-lactones in good yields with good diastereoselectivities and excellent enantioselectivities. Control experiments reveal that the [3+4] cycloadducts are kinetically favored and could be transformed to the thermodynamically favored [3+2] cycloadducts with a non-bifunctional NHC catalyst.

The N-heterocyclic carbene-catalyzed enantioselective [3+3] cyclocondensation of bromoenals and ketimines was developed. The reaction gives the corresponding dihydropyridinones in high yields with high enantioselectivity.

Although the NHC-catalyzed cyclization reactions have been well established for the synthesis of various heterocycles, the corresponding all carbon cyclization reaction for the synthesis of carbocycles is far less established. In this note, the NHC-catalyzed all carbon [4+2] cyclocondensation of α,β-unsaturated acyl chlorides and 3-alkenyloxindoles was developed to give the corresponding spirocarbocyclic oxindoles in good yield with good to high diastereoselectivities.

The catalytic cyclocondensation of in situ activated α,β-unsaturated carboxylic acids was developed. N-heterocyclic carbenes efficiently catalyzed the generation of α,β-unsaturated acyl azolium intermediates from α,β-unsaturated carboxylic acids via in situ generated mixed anhydrides for the enantioselective [3+2] and [3+3] cyclocondensation with α-amino ketones and alkyl(aryl)imines, respectively. The corresponding pyrrolidinones and dihydropyridinones were isolated in good yields with high to excellent enantioselectivities.

Cyclic ketimines were successfully used as electrophiles in phosphane-catalyzed [4+2] annulation reactions with ethyl 2-methyl-2,3-butadienoate to give the corresponding highly substituted tetrahydropyridine derivatives in moderate to good yields (55–73 %), and with moderate to excellent regioselectivity.

In contrast with the reported phosphine- and DABCO-catalyzed [3+2] and [2+2] annulation of allenoates with trifluoromethylketone, the [2+2+2] annulation of allenoates and two molecules of trifluoromethylketone was found under the condition of N-heterocyclic carbene catalysis.

Optically active terminal 1,2-diols were prepared with high enantiopurity via the TMS-quinidine-catalyzed enantioselective cyclization of acyl chlorides and oxaziridine, followed by reductive ring-opening of the cycloadducts.

Highly enantioselective [3+3] annulation reactions of bromoenals and 1,3-dicarbonyl compounds are reported. In addition, both enantiomers of the resultant dihydropyranone could be easily obtained by choosing N-heterocyclic carbenes (NHCs) with the same stereocenter but different substituents under the optimized reaction conditions.

A straightforward synthesis of optically active trifluoromethyl dihydropyranones and spirocyclic oxindole-dihydropyranones has been realized by the chiral N-heterocyclic carbenes-catalyzed cyclization of α,β-unsaturated β-methylacyl chlorides with activated trifluoromethyl ketones or isatin derivatives.

Chiral N-heterocyclic carbenes were found to be efficient catalysts for the formal [2+2] cycloaddition reaction of disubstituted ketenes and isatins to give the corresponding spirocyclic oxindole-β-lactones in good yields with good diastereoselectivities and excellent enantioselectivities. Ring opening with Grignard reagents or decarboxylation of the oxindole spirocyclic-β-lactone gave the corresponding 3-hydroxy- or 3-alkylenyloxindoles in good yields.

Chiral N-heterocyclic carbenes were found to be efficient catalysts for the formal [4+2] cycloaddition reaction of alky(aryl)ketenes and o-quinone methides to give the corresponding 3,3,4-trisubstituted 3,4-dihydrocoumarins in good yields with good diastereoselectivities and excellent enantioselectivities.

A series of chiral N-heterocyclic carbenes (NHCs), derived from L-pyrogutamic acid, were found to be efficient catalysts for the asymmetric dimerization of alkylarylketenes to give the corresponding α-quaternary β-alkylidenyl-β-lactones in good yields with up to 97% ee. A chiral NHC with a proximal hydroxy group is superior in comparison with the corresponding NHC with its hydroxy group protected.