Enantioselective synthesis of spirocyclic cyclopentenes: asymmetric [3+2] annulation of 2-arylideneindane-1,3-diones with MBH carbonates derivatives catalyzed by multifunctional thiourea–phosphines
Graphical abstract
Multifunctional thiourea–phosphine TP3 is a fairly effective catalyst for the enantioselective synthesis of spirocyclic cyclopentenes via asymmetric [3+2] annulation of 2-arylideneindane-1,3-diones with MBH carbonates. The corresponding quaternary carbon centered spirocyclic cyclopentenes were obtained in moderate yields, with high diastereoselectivities and enantioselectivities under mild conditions.
Introduction
1,3-Indanedione and its derivatives constitute a unique group of compounds and attracted much attention of organic chemists and biologists due to their characteristic features.1 Thus far, they have been widely employed in the synthesis of drugs,2 in forensic chemistry for fingerprint detection,3 in dyes and pigments,4 and in semi- and photo-semiconductors,5 proving that 1,3-indanedione and its derivatives are versatile starting materials for the synthesis of potentially important compounds.
Mortia−Baylis−Hillman (MBH) adducts have been also proven to be suitable precursors for the synthesis of multifunctional cyclic compounds, because the in situ generated phosphorus ylides from MBH carbonates in the presence of tertiary phosphines are very reactive 1,3-dipoles in a variety of annulations.6 In this field, Lu and his co-workers first reported a series of intra- and intermolecular [3+n] annulations (n=2, 4, 6) using MBH carbonates as 1,3-dipoles with various electron-deficient olefins catalyzed by a tertiary phosphine, affording the corresponding cycloadducts in good yields and high regioselectivities under mild conditions.7 More recently, Zhang, Huang and He as well as their co-workers have also developed several MBH adducts involved in [4+1] annulations to give the cycloaddition products in high yields, respectively.8
To the best of our knowledge, there are few reports about asymmetric version of this reaction. The first report on the asymmetric intermolecular [3+2] cycloaddition of MBH carbonates with methyleneindolinones was disclosed by Barbas and his co-workers, providing the corresponding spirocyclopentane–oxindoles in good yields and high ee values.9 Then, Lu's group developed l-threonine-derived chiral phosphines and indicated that these chiral catalysts were effective promoters in the asymmetric [3+2] annulation of MBH carbonates with isatylidenemalononitriles to deliver the optically active cyclic products in high yields with high enantioselectivities.10 With regard to the intramolecular [3+2] annulation of MBH carbonates with electron-deficient olefins, Tang and his co-workers first utilized spirobiindane-based chiral phosphines as catalysts to produce the corresponding intramolecular [3+2] cyclic adducts in good yields along with high ee values.11 Moreover, our group has designed and synthesized a series of chiral multifunctional thiourea–phosphine catalysts derived from an axially chiral binaphthyl scaffold and has also demonstrated that these chiral phosphines were very effective catalysts in the asymmetric aza-MBH reaction and asymmetric allylic substitution of MBH adducts, giving the corresponding products in good yields and excellent enantioselectivities as well as in the asymmetric [3+2] annulations of MBH carbonates with isatylidenemalononitriles, giving the desired cycloadducts in good yields along with moderate enantioselectivities.12, 13, 14 Recently, we have further developed a series of multifunctional thiourea–phosphine catalysts derived from natural amino acid and applied them in asymmetric [3+2] annulation of MBH carbonates with trifluoroethylidenemalonates to give corresponding highly functionalized trifluoromethyl or pentafluoroethyl-bearing cyclopentenes in excellent yields (upto >99%), high diastereoselectivities (upto 99:1) and enantioselectivities (upto 96%) under mild conditions.15 Herein as a part of our continuing interest in asymmetric annulation catalyzed by multifunctional thiourea–phosphines, we wish to report the asymmetric annulation of 2-arylideneindane-1,3-diones 1 with MBH carbonates 2 catalyzed by multifunctional thiourea–phosphines to afford the corresponding quaternary carbon centered spirocyclic cyclopentenes in moderate yields, high diastereoselectivities, and enantioselectivities under mild conditions.16
Section snippets
Results and discussion
Initially, we examined the reaction of 2-(4-nitrobenzylidene)indan-1,3-dione 1a (0.1 mmol, 1.0 equiv) with MBH carbonate 2a (0.2 mmol, 2.0 equiv) catalyzed by PPh3 in THF (2 mL) at room temperature, the C-1 addition product 3a was obtained in 74% yield along with excellent diastereoselectivities (upto >99% dr) within 24 h. Based on the preliminary investigation on [3+2] annulation of 2-(4-nitro-benzylidene)-indan-1,3-dione 1a with MBH carbonate 2a, asymmetric version of this reaction was
General remarks
Melting points were determined on a digital melting point apparatus and temperatures were uncorrected. Optical rotations were determined at 589 nm (sodium D line) by using a Perkin–Elmer-341 MC digital polarimeter; [α]D-values are given in unit of 10 deg−1 cm2 g−1 1H NMR spectra were recorded on a Varian Mercury-300 and 400 spectrometer for solution in CDCl3 with tetramethylsilane (TMS) as an internal standard; coupling constants J are given in Hertz. 13C NMR spectra were recorded on a Varian
Acknowledgements
We thank the Shanghai Municipal Committee of Science and Technology (11JC1402600), National Basic Research Program of China (973)-2010CB833302, the Fundamental Research Funds for the Central Universities and the National Natural Science Foundation of China for financial support (21072206, 20872162, 20672127, 20732008, 21121062, and 20702013).
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