An Efficient Four‐component Synthesis of Spiro[indoline‐pyrazolo[4′,3′:5,6]pyrido[2,3‐d]pyrimidine]triones

A four‐component reaction in the presence of Alum [KAl(SO₄)₂·12H₂O] as an inexpensive and reusable catalyst using the ionic liquid as an effective green reaction media is reported.     

Aza‐Quaternary Scaffolds from Selective Bond Cleavage of Bridgehead‐Substituted 7‐Azabicyclo[2.2.1]heptane: Total Synthesis of (+)‐Cylindricines C–E and (−)‐Lepadiformine A

A novel bridgehead‐substituted aza‐bicyclic framework has been designed and developed in both enantiomeric forms through an asymmetric desymmetrization reaction. Strategic exploitation of the ring strain in the aza‐bicyclic framework has been utilized for the construction of the chiral aza‐quaterenary scaffolds by selective bond fragmentation processes. Furthermore, a strategically designed precursor is employed for selective bond cleavage to initiate a cascade rearrangement for the total synthesis of the 1‐azaspirotricyclic marine alkaloids (+)‐cylindricines C, D, and E, as well as (?)‐lepadiformine A. An oxidation/retro‐aldol/aza‐Michael sequence generated three new chiral centers with the required configuration in one pot.     

Stereocontrolled Synthesis of Spiro[n.2]alkenes by Ring Contraction of Fused‐Cyclobutanols

An unusual ring‐contraction rearrangement to give spirocyclopropanes from fused cyclobutanols (see scheme) has been developed. It is found that the strain energy of the substrates derived from an additional fused ring and the stereoelectronic effect of the migrating σ bond are important factors. It is noteworthy that the rearrangement proceeds in a stereospecific manner. Moreover, the method provides a spiro(cyclopropane–indane) framework from tricyclo[6.3.0.02,5]undecane, which corresponds to illudane and the protoilludane skeleton.     

Highly Enantioselective Tandem Michael Addition of Tryptamine‐Derived Oxindoles to Alkynones: Concise Synthesis of Strychnos Alkaloids

A highly enantioselective tandem Michael addition of tryptamine‐derived oxindoles to alkynones was developed by taking advantage of a chiral N,N′‐dioxide Sc(OTf)₃ catalyst. The reaction enables the facile preparation of enantioenriched spiro[pyrrolidine‐3,3′‐oxindole] compounds, which provides a novel strategy for the synthesis of monoterpenoid indole alkaloids. As a demonstration, the asymmetric synthesis of strychnos alkaloids [(?)‐tubifoline, (?)‐tubifolidine, (?)‐dehydrotubifoline] was achieved in 10–11 steps.     

新型色满酮并环己烷螺环氧化吲哚类化合物的合成

以色酮 氧化吲哚合成子与硝基苯乙烯,在催化剂DBU作用下,在二氯甲烷中发生Michael/Michael加成环化反应,合成了9个未见文献报道的新型色满酮并环己烷螺环氧化吲哚类化合物3a~3i产率72%~87%, dr值4/1~2/1, 其结构经¹H NMR, ¹³C NMR和HR-MS（ESI-TOF）表征确定。     

Convenient Synthesis of Spiro[benzo[d]pyrrolo[2,1‐b]thiazole‐3,2′‐indenes] Derivatives via Three‐Component Reaction

The three‐component reaction of N‐phenacylbenzothiazolium bromides, aromatic aldehydes and indane‐1,3‐dione in ethanol at room temperature in the presence of triethylamine as base afforded functionalized spiro[benzo[d]pyrrolo[2,1‐b]thiazole‐3,2′‐indenes] in good yields and with high diastereoselectivity. The ¹H NMR data and single crystal structure clearly indicated that the obtained spiro compounds predominately have one diastereoisomer.     

Synthesis and Antiviral Properties of Spirocyclic [1,2,3]‐Triazolooxazine Nucleosides

An efficient synthesis of spirocyclic triazolooxazine nucleosides is described. This was achieved by the conversion of β‐D ‐psicofuranose to the corresponding azido‐derivative, followed by alkylation of the primary alcohol with a range of propargyl bromides, obtained by Sonogashira chemistry. The products of these reactions underwent 1,3‐dipolar addition smoothly to generate the protected spirocyclic adducts. These were easily deprotected to give the corresponding ribose nucleosides. The library of compounds obtained was investigated for its antiviral activity using MHV (mouse hepatitis virus) as a model wherein derivative 3 f showed the most promising activity and tolerability.     

Expanding the Scope of Enantioselective FerroPHANE‐Promoted [3+2] Annulations with α,β‐Unsaturated Ketones

The planar chiral 2‐phospha[3]ferrocenophane I has been shown to be the first efficient nucleophilic organocatalyst for the enantioselective synthesis of cyclopentenylphosphonates, through [3+2] cyclizations between diethyl allenylphosphonate and α,β‐unsaturated ketones. The same catalyst has also been applied to the highly enantioselective [3+2] cyclizations of allenic esters with dibenzylideneacetone and analogous bis‐enones, leading to functionalised cyclopentenes with either monocyclic or spirocyclic structures (ee 84–95 %). It has been shown that the residual enone functions in the resulting cyclopentenes can be involved in subsequent cyclization steps to afford unprecedented C₂‐symmetric bis‐cyclopentenylketones. In order to provide insight into the behaviour of FerroPHANE I as a chiral catalyst in [3+2] cyclisations, the energetically most favoured isomers of the key phosphine‐allene adduct have been calculated by DFT methods. Factors likely to control the chiral induction process are highlighted.     

Development of Chiral Spiro Phosphoramidites for Rhodium-Catalyzed Enantioselective Reactions

A series of 1,1′-spirobiindane-7,7′-diol ( SPINOL ) analogues bearing a 2,2′-dimethyl-, cyclopentyl-, or cyclohexyl-fused ring were synthesized, and their distinct structural features were elucidated by X-ray crystallography. On the basis of these scaffolds, chiral monophosphoramidite ligands 6 a – m were synthesized, which demonstrated excellent enantioselectivity in Rh^I-catalyzed asymmetric hydrogenation of a dehydro amino acid methyl ester. Ligands 6 a – m were also successfully applied in the Rh^I-catalyzed enantioselective [4+2] cycloaddition of α,β-unsaturated imines with isocyanates, which afforded the corresponding pyrimidinones in good yields (60–92 %) with high enantioselectivities (75–92 % ee).     

Efficient Synthesis of the Functionalized Spiro[indoline‐3,4′‐pyridine] via Four‐component Reaction

An efficient synthetic procedure for the functionalized spiro[indoline‐3,4′‐pyridine] was developed via the four‐component reactions of arylamines, acetylenedicarboxylates, isatins and malononitrile with triethylamine as the base catalyst. The advantages of this reaction are using common starting material, mild reaction conditions, broad scope of reactants and operational simplicity.     

Efficient Synthesis of Spiro[furan‐3,3′‐indoline] Derivatives via Reactions of Pyridinium Salts with Isatinylidene Acetoacetates

An efficient synthetic procedure for the functionalized spiro[furan‐3,3′‐indoline] derivatives was successfully developed by domino reactions of N‐phenacylpyridinium bromides or N‐ethoxycarbonylmethylenepyridinium bromide with isatinylidene acetoacetate in the presence of triethylamine in ethanol at room temperature. The mechanism included sequential Michael addition of the in situ generated pyridinium ylide and intramolecular substitution of enolate.