Reactivity of spiroanthraceneoxazolidines with cyclopropanes: An approach to the oxindole alkaloid scaffold

The reaction of N-methylspiro[anthracene-oxazolidine] with spiro[cyclopropane-3,3′-indolin]-2-ones in the presence of MgI₂ formed the corresponding spiro[pyrrolidine-3,3′-indolin]-2-ones in 42–65% yields. The use of N-benzylspiro[anthracene-oxazolidine] in this reaction led to the formation of a mixture of the corresponding N-methyl- and N-benzylpyrrolidines.     

Synthesis and transformations of metallacycles 44. Cycloalumination of methylenecyclobutane terpene derivatives with Et3Al catalyzed by Cp<Subscript>2</Subscript>ZrCl<Subscript>2</Subscript>

Cycloalumination of methylenecyclobutane terpene derivatives (d(+)-camphor, (+)-camphene, β-pinene, and l(–)-menthol) with Et₃Al catalyzed by Cp₂ZrCl₂ produced novel spirofused organoaluminum compounds in high yields. The synthesized compounds were in situ transformed into the corresponding spiro tetrahydroselenophenes and spiro phospholanes.     

XY-ZH compounds as potential 1,3-dipoles. Part 63: Silver catalysed azomethine ylide cycloaddition—the synthesis of spiro homoserine lactone analogues

A range of room temperature 1,3-dipolar cycloaddition reactions of imines of 2-amino-γ-lactone and thiolactone, catalysed by a combination of AgOAc or Ag₂O with NEt₃ or DBU, are described. The spiro lactones/thiolactones are formed regio- and stereoselectively as single cycloadducts in good yield via the syn dipoles and an endo-transition states.     

Asymmetric aldol reactions catalyzed by new spiro diamine derivatives

Two new organocatalysts derived from l-proline and a novel chiral spiro diamine bearing a C₂ symmetric backbone, were introduced for an asymmetric aldol reaction in moderate to good asymmetric induction in up to 76% ee and high yields.     

A one-pot three-component reactions for the synthesis of fully substituted spiro indeno[1,2-b]quinoxaline derivatives

An efficient and simple approach of the synthesis of some spiro indeno[1,2-b]quinoxalines via a one-pot three-component reaction of 11H-indeno[1,2-b]quinoxalin-11-one, pyrazolone, and malononitrile in the presence of Na₂CO₃ at 70 °C is reported. This reaction has shown to have high atom economy.     

Absolute configuration and conformation of 1,1′-spirobi [benz[f] indan]

Three diastereomers of (1S) 3-3′-di-t-butyl-1,1′-spirobi [benz[f] indan] have been prepared. In the ¹B_b region all the isomers showed typical c.d. couplets of negative sign, reflecting the identity of configuration at the spiro center irrespective of their different conformations.     

A facile and efficient one-pot synthesis of thiirans by the reaction of benzoxazolyl β-ketosulfides with NaBH4/NaOH

Convenient and efficient procedures for thiirans have been developed via a one-pot reaction of benzoxazolyl β-ketosulfides with NaBH₄ and NaOH in MeOH and THF. The reaction is considered to proceed via the spiro intermediate by the ipso-addition of β-hydroxygroup, which is formed by the NaBH₄ reduction of β-keto group, to 2-position of benzoxazole group.     

Mn(III)-promoted synthesis of spiroannular tricyclic scaffolds via sulfonylation/dearomatization of biaryl ynones

A Mn(III)-promoted radical oxidative ipso-annulation reaction of biaryl ynones with sodium sulfinates to construct various substituted spiro[5.5]trienones has been explored in this study. This protocol is characterized by mild reaction conditions, good substrates functional group compatibility, cheap and easily prepared Mn(OAc)₃·2H₂O, and it demonstrates a simple operation.     

Addition initiated ring closure substituted spiro[4,2]Hepta-1,3-dienes via fulvene intermediates

The reactivity of the epoxy-fulvene 1 with various nucleophiles has been examined. It is a versatile Intermediate for the preparation of spiro[4.2]hepta-1,3-diene synthons via nucleophilic addition to the C₆ position followed by intramolecular cyclization of the substituted cyclopentadiene anion generated in situ.     

Angular Distortions at Tetracoordinate Carbon Planoid Configurations in Substituted Spiro[4.4]nonanes

The configuration of the spiro centre in polycyclic compounds containing a spiro[4.4]nonane substructure is analyzed in terms of symmetry coordinates. As revealed by X-ray structures of such compounds, the local distortions around the quaternary C-atom are dominated by a decrease of the ring-bond angles at the spiro centre and a twist of one ring relative to the other. The planoid deformations given by the planarization index P_C are comparatively small for spiro[4.4]nonanes, which contain either no additional bridges between the rings or only α,β′–or β,β′-polymethylene bridges. This indicates that the local strain in the spiro C(C)₄ fragments is rather small.     

Isatins 3-C annulation vs ring-opening: Two different pathways for synthesis of spiro compounds via multicomponent reactions

An efficient synthesis of spiro compounds via two different pathways from the reactions of isatins, 3-phenylisoxazol-5(4H)-one (3-ethylisoxazol-5(4H)-one), and pyrazol-5-amine (6-aminopyrimidine-2,4(1H,3H)-dione) were reported. The catalyst Amberlyst-15 could be easy recycled and reused for many time without any appreciable loss in catalytic activity. The new type spiro compounds were gained through the ring-opening of isatins process. The structures of spiro[indoline-3,4′-isoxazolo[5,4-b]pyrazolo[4,3-e]pyridin]-2-one, spiro[isoxazolo[5,4-b]quino line-4,5′-pyrrolo[2,3-d]pyrimidine]-2′,4′,6′(1′H,3′H,7′H)-trione, and spiro[indoline-3,4′-pyrazolo[3,4-b]pyridine]-2,6′(5′H)-dione were successfully confirmed by ¹H NMR, ¹³C NMR, HRMS, and X-ray crystal diffraction analysis.     

Reactions of platinum complexes with spiro compounds. formation of platinospiroalkanes

Spiro[2.nalkanes (n = 2, 4, 5) react with platinum complexes to form compounds of composition PtCl₂(spiroalkane). These materials have been characterized by infrared and nuclear magnetic resonance spectra, and the point of insertion has been shown to be the cyclopropyl carbon—carbon bond opposite the spiro carbon.     

Catalytic asymmetric brominative dearomatization reaction of benzofurans

A catalytic asymmetric brominative dearomatization reaction of benzofuran derivatives was achieved by using hydroquinidine 1,4-phthalazinediyl diether [(DHQ)₂PHAL] as the catalyst and N-bromoacetamide (NBAc) as the brominating reagent. A series of brominated spiro[benzofuran-2,5'-oxazoles] bearing two contiguous stereogenic centers were obtained in high yields (up to 99%) with excellent enantioselectivity (up to 97% ee).     

Synthesis of novel spiro[benzo[4,5]thiazolo[3,2-a]chromeno[2,3-d]pyrimidine-14,3′-indoline]-1,2′,13(2H)-triones via three component reaction

A new and efficient method for the synthesis of hitherto unreported spiro[benzo[4,5]thiazolo[3,2-a]chromeno[2,3-d]pyrimidine-14,3′-indoline]-1,2′,13(2H)-triones was developed via the Domino Knoevenagel condensation–Michael addition–intermolecular cyclization sequences of isatin derivatives, cyclohexane-1,3-diones, and 2-hydroxy-4H-benzo[4,5]thiazolo[3,2-a]pyrimidin-4-ones, employing 12-tungstophosphoric acid (H₃PW₁₂O₄₀) as an effective and inexpensive catalyst.     

Rhodium(III)-catalyzed ring-opening of strained olefins through C–H activation of O-acetyl ketoximes: an efficient synthesis of trans-functionalized cyclopentenes and spiro[2.4]heptenes

An efficient strategy for the stereoselective synthesis of functionalized cyclopentenes and spiro[2.4]heptenes from strained olefins via C–H activation of aryl ketone O-acetyl ketoximes using [RhCl₂Cp^∗]₂ catalyst is described. The results revealed that a wide range of readily accessible aryl and heteroaryl ketoximes are compatible in this method for the ring opening of bicyclic and spirotricyclic olefins.     

NMR study of the inversion at carbon 2 of some 1′3′3′-trimethylindolino disubstituted spirobenzopyranes

The ¹H NMR spectra of some 1′3′3′-trimethylindolino-6,8-disubstituted-spirobenzopyranes in equilibrium with more than 5% of their merocyanine isomer were taken at different temperatures in dimethylsulfoxide d₆. This presents evidence of a fast inversion process at the asymmetric spiro carbon-2. It is shown that the intermediate responsible for the inversion process is certainly not the merocyanine but more likely the open ring cis isomer of the spiropyran.     

Exploring structural effects of ketone catalysts on asymmetric epoxidation of olefins

Several ketone catalysts containing spiro ethers and lactones have been investigated for the asymmetric epoxidation of olefins. The results showed that substituents on the spiro ring of the ketone catalysts have profound effects on enantioselectivity. Results also suggested that the high enantioselectivities previously observed for conjugated cis-olefins with oxazolidinone containing ketones could be partially due to attractive interactions between the R_π group of the olefin and the carbonyl group of the oxazolidinone. In addition, nonbonding interactions such as van der Waals forces and/or hydrophobic interactions between the olefin substituents and the nitrogen substituents of the oxazolidinone may also be involved in stereodifferentiation. The information gained provides additional understanding of factors important for ketone catalyzed epoxidations.     

Design and synthesis of spiro bis(1,2,3-triazolium) salts as chiral ionic liquids

Room temperature chiral spiro ionic liquids 1 and 2 based on 1,2,3-triazolium salts, were synthesized via an intramolecular double Huisgen reaction. The preparation of the enantiomerically pure spiro triazolium salts was achieved by resolution by HPLC using a chiral stationary phase column and subsequent N-dialkylations of spiro triazoles 6 and 10.     

Synthesis of spiro ?,ζ-D-CNA in xylo configuration featuring noncanonical δ/?/ζ torsion angle combination

The synthesis of diastereoisomers of spiro xylo-?,ζ-D-CNA dinucleotide building units of nucleic acids, in which the ? and ζ torsional angles are stereocontrolled by a dioxaphosphorinane ring structure (D-CNA family), is described from uridine with a Mukaïyama's aldol condensation as key reaction. The NMR structure analysis showed that δ, ? and ζ torsional angles of the (S_C3′,R_P)- and (S_C3′,S_P)-configured xylo-?,ζ-D-CNA TT dimer are restricted to the {δ, ?, ζ}={cis, trans, gauche(+)} or {cis, trans, gauche(−)} conformation, respectively, that are significantly different from those typically observed in A- or B-type duplexes.     

New reactions of 2,3-diaminonaphthaline with carbonyl electrophiles

The reaction of 2,3-diaminonaphthalene with dimedone gave 3-[(3-amino-2-naphthyl)amino]-5,5-dimethylcyclohex-2-en-1-one that reacts with alloxan to afford a product of addition at the enamine moiety. The latter is converted to a spiro derivative on heating in CF₃COOH, or undergoes condensation with 2,6-di-tert-butyl-p-benzoquinone to give a benzophenazinone derivative with a sterically hindered phenol substituent.