Synthesis of Cyclopropenes and Fluorinated Cyclopropanes via Michael Initiated Ring Closure of Alkyl Triflones.

A facile synthesis of cyclopropenes and fluorinated cyclopropanes from readily available alkyl triflones was developed. The reaction, regardless of electronic effect, gave products in good to excellent yields and moderate diastereoselectivity. The mechanism may involve tandem Michael addition of triflones/intramolecular nucleophilic cyclization (elimination of -SO2 CF3 )/elimination of fluoride.

Selective Synthesis of 3-(9 H-Carbazol-2-yl)indolin-2-ones and Spiro[tetrahydrocarbazole-3,3'-oxindoles] via a HOTf Catalyzed Three-Component Reaction.

A HOTf catalyzed three-component reaction of indoles, acetophenones, and ( E)-3-phenacylideneoxindolinones resulted in the unexpected polysubstituted 3-(9 H-carbazol-2-yl)indolin-2-ones in good yields. A similar reaction with various cyclic ketones afforded the corresponding carbocyclic fused 3-(9 H-carbazol-2-yl)indolin-2-ones. On the other hand, ( E)-3-arylideneoxindolinones in the three-component reaction gave the expected spiro[tetrahydrocarbazole-3,3'-oxindoles] through a domino alkenylation/Diels-Alder reaction. The unusual different reactivity of ( E)-3-phenacylideneoxindolinones and ( E)-3-arylideneoxindolinones in the three-component reactions was believed to involve the different reaction paths caused by the existence of the carbonyl group.

Synthesis of functionalized dispiro[indoline-3,1[Formula: see text]-cyclopentane-3[Formula: see text],3[Formula: see text]-indolines] via cyclodimerization of 3-phenacylideneoxindolines with benzoylhydrazides and arylhydrazines.

The triethylamine-promoted domino cyclodimerization reaction of 3-phenacylideneoxindolines with benzohydrazides in acetonitrile afforded densely substituted dispiro[indoline-3,1[Formula: see text]-cyclopentane-3[Formula: see text],3[Formula: see text]-indolines] in good yields and with high diastereoselectivity. The similar domino reaction of 3-phenacylideneoxindoles with arylhydrazines also gave corresponding dispiro[indoline-3,1[Formula: see text]-cyclopentane-3[Formula: see text],3[Formula: see text]-indolines] with hydrazinyl or arylazo groups according to the structures of arylhydrazines.

TfOH-Catalyzed One-Pot Domino Reaction for Diastereoselective Synthesis of Polysubstituted Tetrahydrospiro[carbazole-1,3'-indoline]s.

TfOH-catalyzed one-pot sequential reaction of indoles, acetophenones (cyclic ketones), and various 3-methyleneoxindolines in toluene afforded polysubstituted tetrahydrospiro[carbazole-1,3'-indoline]s in satisfactory yields. 1H NMR spectra and single-crystal structures indicated that the obtained tetrahydrospiro[carbazole-1,3'-indoline]s existing in an unusual trans-configuration. The reaction mechanism was believed to proceed with domino acid-catalyzed 3-alkenylation of indoles with acetophenones, Diels-Alder reaction of 3-alkyenylindoles with 3-methyleneoxindolines, and an acid-catalyzed diastereoisomerization process.

Selective construction of polycyclic spirooxindoles via a Cu(OTf)2/HOTf-catalyzed domino reaction of o-arylalkynylacetophenones and 3-phenacylideneoxindoles.

Under the combined catalysis of Cu(OTf)2/HOTf, the domino annulation reaction of o-arylalkynyl acetophenones with 3-phenacylideneoxindoles in refluxing acetonitrile selectively afforded functionalized spiro[indoline-3,7'-tetrapheno[7,6-bc]furans] and spiro[indeno[1,2-b]naphtho[2,1-d]furan-7,3'-indolines] depending on the electronic effect of the substituents on both substrates.

Chameleonic Reactivity of Imidoyl Sulfoxonium Ylides: Access to Functionalized Pyrroles and Dihydro-pyridines.

We have found a chameleonic reactivity of imidoyl sulfoxonium ylides. On the one hand, imidoyl sulfoxonium ylides react with electron-deficient reagents, such as alkynyl esters, to lead to the formation of 1,2-dihydro-pyridines. The methyl group attached to the sulfur atom acts as a methylene donor. On the other hand, imidoyl sulfoxonium ylides react with pyridinium 1,4-zwitterionic thiolates, which leads to the formation of functionalized pyrroles. Both transformations feature mild reaction conditions and good functional group tolerance.

Synthesis of ArCF2X and [18F]Ar-CF3 via Cleavage of the Trifluoromethylsulfonyl Group.

A versatile synthesis of ArCF2X and [18F]Ar-CF3 type compounds from readily available ArCF2SO2CF3 has been developed. Diverse nucleophiles, including weak nucleophiles such as halides (18F-, Cl-, Br-, and I-), RSH, and ROH, could react with ArCF2SO2CF3 efficiently to give the corresponding difluoromethylene products. The control experiments and the Hammett plot indicated that the reaction might proceed through a difluorocarbocation intermediate generated from the steric hindrance-assisted cleavage of the trifluoromethylsulfonyl group.

Chemo-, regio- and stereoselective synthesis of monofluoroalkenes via a tandem fluorination-desulfonation sequence.

A widely applicable approach for the synthesis of Z-monofluoroalkenes from readily available alkyl triflones and NFSI has been reported. The reaction proceeded under mild conditions, affording mono-fluorinated alkenes in good to excellent yields with excellent chemo- regio- and stereoselectivity. The mechanism may involve electrophilic fluorination of triflones followed by the highly stereoselective concerted bimolecular elimination (E2) of CF3SO2H.

Base promoted gem-difluoroolefination of alkyl triflones.

A new synthesis of gem-difluoroalkenes from readily available alkyl triflones and difluorocarbene precursors such as TMSCF2Br has been reported. The reaction, regardless of electronic effect, gives gem-difluoroalkenes in good to excellent yields. The mechanism may involve deprotonation of triflones, nucleophilic addition, and the elimination of SO2CF3.

HOAc-Mediated Domino Diels-Alder Reaction for Synthesis of Spiro[cyclohexane-1,3'-indolines] in Ionic Liquid [Bmim]Br.

An efficient and diastereoselective synthetic protocol for the construction of spiro[cyclohexane-1,3'-indolin]-3-en-2'-ones and spiro[cyclohexane-1,2'-inden]-3-ene-1',3'-diones was provided by HOAc-mediated domino reaction of pinacoles with typical dienophiles, such as 3-methyleneoxindolines and 2-arylideneindane-1,3-diones, in ionic liquid [Bmim]Br. This domino reaction involved the in situ generation of 1,3-dienes from acid-mediated dehydration of various pinacoles and the sequential Diels-Alder reaction.

Stepwise cycloaddition reaction of N-phenacylbenzothiazolium bromides and nitroalkenes for tetrahydro-, dihydro- and benzo[d]pyrrolo[2,1-b]thiazoles.

The triethylamine promoted stepwise 1,3-dipolar cycloaddition reaction of N-phenacylbenzothiazolium bromides with nitroalkenes in ethanol resulted in a mixture of two isomeric tetrahydrobenzo[d]pyrrolo[2,1-b]thiazoles with cis/trans/cis- and all-trans-configurations. More importantly, the corresponding dihydrobenzo[d]pyrrolo[2,1-b]thiazoles can be selectively prepared in refluxing ethanol and the benzo[d]pyrrolo[2,1-b]thiazoles can be obtained in satisfactory yields by sequential dehydrogenation with DDQ as oxidizer. On the other hand, the similar cycloaddition reaction of N-phenacylbenzothiazolium bromides with 1-methy-1-nitroalkenes in refluxing ethanol afforded benzo[d]pyrrolo[2,1-b]thiazoles with splitting out of nitro group. The stereochemistry of the spiro compounds was clearly elucidated on the basis of NMR spectra and sixteen single crystal structures.