Polymer-Supported 2,2′-Bis(oxazolin-2-yl)-1,1′-binaphthyls (Boxax): Immobilized Chiral Ligands for Asymmetric Wacker-Type Cyclizations

Abstract

Homochiral 2,2′-bis(oxazolin-2-yl)-1,1′-binaphthyl (boxax) ligands were anchored on various polymer supports including PS-PEG, PS, PEGA, and MeO-PEG via selective monofunctionalization at the 6-position of the binaphthyl backbone. Palladium(II) complexes of the supported boxax ligands catalyzed Wacker-type cyclization of 2-(2,3-dimethyl-2-butenyl)phenol to give 2-methyl-2-isopropenyl-2,3-dihydrobenzofuran with up to 96% ee.

boxax - immobilized chiral catalysts - asymmetric catalysis - Wacker-type cyclization

References

For reviews, see:

<A NAME="RG24902ST-1A">1a</A> Bailey DC. Langer SH. Chem. Rev.  1981,  81:  109 

<A NAME="RG24902ST-1B">1b</A> Shuttleworth SJ. Allin SM. Sharma PK. Synthesis  1997,  1217 

<A NAME="RG24902ST-1C">1c</A> Burgess K. Porte AM. In Advances in Catalytic Processes   Doyle MP. JAI Press; Greenwich: 1997.  2:  p.69 

<A NAME="RG24902ST-1D">1d</A> Shuttleworth SJ. Allin SM. Wilson RD. Nasturica D. Synthesis  2000,  1035 

<A NAME="RG24902ST-1E">1e</A> Dörwald FZ. Organic Synthesis on Solid Phase   Wiley-VCH; Weinheim: 2000. 

For studies on polymer-supported palladium catalysts reported by the author’s group, see:

<A NAME="RG24902ST-2A">2a</A> π-Allylic substitution: Uozumi Y. Danjo H. Hayashi T. Tetrahedron Lett.  1997,  38:  3557 

<A NAME="RG24902ST-2B">2b</A> Asymmetric allylic substitution: Uozumi Y. Danjo H. Hayashi T. Tetrahedron Lett.  1998,  39:  8303 

<A NAME="RG24902ST-2C">2c</A> π-Allylic substitution: Danjo H. Tanaka D. Hayashi T. Uozumi Y. Tetrahedron  1999,  55:  14341 

<A NAME="RG24902ST-2D">2d</A> Cross-coupling: Uozumi Y. Danjo H. Hayashi T. J. Org. Chem.  1999,  64:  3384 

<A NAME="RG24902ST-2E">2e</A> Carbonylation reaction: Uozumi Y. Watanabe T. J. Org. Chem.  1999,  64:  6921 

<A NAME="RG24902ST-2F">2f</A> Asymmetric allylic substitution: Uozumi Y. Shibatomi K. J. Am. Chem. Soc.  2001,  123:  2919 

<A NAME="RG24902ST-2G">2g</A> Cross-coupling: Uozumi Y. Nakai Y. Org. Lett.  2002,  4:  2997 

<A NAME="RG24902ST-2H">2h</A>

Sonogashira reaction: Uozumi, Y.; Kobayashi, Y. Heterocycles 2002, in press

<A NAME="RG24902ST-3">3</A> Chiral Catalyst Immobilization and Recycling   De Vos DE. Vankelecom IFJ. Jacobs PA. Wiley-VCH; Weinheim: 2000. and references cited therein

<A NAME="RG24902ST-4">4</A> Uozumi Y. Kyota H. Kishi E. Kitayama K. Hayashi T. Tetrahedron: Asymmetry  1996,  7:  1603 

<A NAME="RG24902ST-5A">5a</A> Uozumi Y. Kato K. Hayashi T. J. Am. Chem. Soc.  1997,  119:  5063 

<A NAME="RG24902ST-5B">5b</A> Uozumi Y. Kato K. Hayashi T. J. Org. Chem.  1998,  63:  5071 

<A NAME="RG24902ST-5C">5c</A> Uozumi Y. Kyota H. Hayashi T. J. Org. Chem.  1999,  64:  1621 

<A NAME="RG24902ST-6">6</A> For a recent review of solid-phase reactions using palladium catalysts, see: Uozumi Y. Hayashi T. Solid-Phase Palladium Catalysis for High-throughput Organic Synthesis, In Handbook of Combinatorial Chemistry   Nicolaou KC. Hanko R. Hartwig W. Wiley-VCH; Weinheim: 2002.  p.531-584  

For recent examples of the immobilization of binaphthyl-based chiral catalysts, see:

<A NAME="RG24902ST-7A">7a</A> Nozaki K. Itoi Y. Shibahara F. Shirakawa E. Ohta T. Takaya H. Hiyama T. J. Am. Chem. Soc.  1998,  120:  4051 

<A NAME="RG24902ST-7B">7b</A> Nozaki K. Itoi Y. Shibahara F. Shirakawa E. Ohta T. Takaya H. Hiyama T. Bull. Chem. Soc. Jpn.  1999,  72:  1911 

<A NAME="RG24902ST-7C">7c</A> Bayston DJ. Fraser JL. Ashton MR. Baxter AD. Polywka MEC. Moses E. J. Org. Chem.  1998,  63:  3137 

<A NAME="RG24902ST-7D">7d</A> Kobayashi S. Kusakabe K. Ishitani H. Org. Lett.  2000,  2:  1225 

<A NAME="RG24902ST-7E">7e</A> Fujii A. Sodeoka M. Tetrahedron Lett.  1999,  40:  8011 

<A NAME="RG24902ST-7F">7f</A> Matsunaga S. Ohshima T. Shibasaki M. Tetrahedron Lett.  2000,  41:  8473 

<A NAME="RG24902ST-7G">7g</A> Nogami H. Matsunaga S. Kanai M. Shibasaki M. Tetrahedron Lett.  2001,  42:  279 

<A NAME="RG24902ST-7H">7h</A> Takamura M. Funabashi K. Kanai M. Shibasaki M. J. Am. Chem. Soc.  2001,  123:  6801 ; see also ref.

<A NAME="RG24902ST-8A">8a</A> Kawashima M, and Kakayama M. inventors; Japan Patent J P  200044504.  ; assigned to Kankyo Kagaku Center K.K., Japan.

<A NAME="RG24902ST-8B">8b</A> De Vanis J.-BR. Tetrahedron Lett.  2001,  42:  6507 

<A NAME="RG24902ST-9">9</A> During preparation of this manuscript, controlled mono-bromination of 1,1′-bi-2-naphthol via the monopivalate 9 was reported, see: Cai D. Larsen RD. Reider PJ. Tetrahedron Lett.  2002,  43:  4055 

<A NAME="RG24902ST-10">10</A>

The enantiomeric purity of (S)-12 and (S)-14 were determined to be both >98% by HPLC analysis using chiral stationary phase column (Daicel Chiracel OD-H, eluent:
n-hexane-isopropanol = 10:1).

<A NAME="RG24902ST-11A">11a</A> Hotta H. Suzuki T. Miyano S. Inoue Y. J. Mol. Cat.  1989,  54:  L5 

<A NAME="RG24902ST-11B">11b</A> Ohta T. Ito M. Inagaki K. Takaya H. Tetrahedron Lett.  1993,  34:  1615 

<A NAME="RG24902ST-12">12</A>

Compounds 17a-c were obtained as single diastereomers.

<A NAME="RG24902ST-13">13</A>

Specific rotation data of 18a-d: 18a: [α]_D ²⁵ -97.75 (c 0.75, THF). 18b: [α]_D ²⁵ -16.93 (c 0.48, THF). 18c: [α]_D ²⁵ -54.95 (c 0.58, THF). 18d: [α]_D ²⁵ -7.28 (c 0.49, THF).

<A NAME="RG24902ST-14">14</A>

ArgoGel amino resin (1% DVB cross-linked) purchased from Argonaut Technologies Inc. was used.

<A NAME="RG24902ST-15">15</A>

Aminomethylated polystyrene (1% DVB cross-linked) was purchased from Novabiochem.

<A NAME="RG24902ST-16">16</A> For a copolymerisate of acrylamidopropyl[2-amino-propyl]polyethylene glycol and N,N-dimethylacrylamide crosslinked with bis(2-acrylamidopropyl)poly(ethylene glycol) (PEGA), see: Meldal M. Tetrahedron Lett.  1992,  33:  3077 

<A NAME="RG24902ST-17">17</A>

MeO-PEG5000 amino resin was purchased from Fluka.

For reviews of PEG-supported reagents, see:

<A NAME="RG24902ST-18A">18a</A> Sieber F. Wentworth P. Janda KD. J. Comb. Chem.  1999,  1:  540 

<A NAME="RG24902ST-18B">18b</A> Wentworth P. Janda KD. Chem. Commun.  1999,  1917 

<A NAME="RG24902ST-18C">18c</A> Toy PH. Janda KD. Acc. Chem. Res.  2000,  33:  546 

<A NAME="RG24902ST-19A">19a</A>

Immobilization of Boxax Ligands: A typical procedure is given for the preparation of the PS-PEG resin-supported ligand 4. Boxax methyl ester 18 and LiOH·H₂O (1.05 equiv to methyl ester) was stirred in a mixture of THF/H₂O at 25 °C for 24 h. After removal of the solvent in vacuo a white precipitate 19 was obtained. A mixture of 19 (1.1 equiv to an amino residue of resin), HOBt (1.0 equiv) and EDCI (2.5 equiv) and PS-PEG amino resin in DMF was shaken at 25 °C for 12 h. To a reaction mixture was added EDCI (5 equiv) and the mixture was continuously shaken for an additional 24 h during which the progress of the reaction was monitored by a Kaiser test. [19b] The reaction mixture was filtered and the resin beads were rinsed with DMF, MeOH and DCM to give a polymer resin supported boxax ligand. A negative Kaiser test and ¹³C-MASNMR studies indicated the complete consumption of the terminal amino residue of the starting resin and the exclusive formation of the desired PS-PEG supported boxax ligands. The loading value of the polymer-supported boxax ligands 4a-d were estimated to be 0.35 mmol/g based on the initial loading value of the amino residue. ¹³C-MASNMR data of 4a-d: 4a: δ = 17.92, 18.25, 31.35, 32.36, 37.33, 39.01, 69.64, 72.08, 124.86, 125.39, 131.29, 132.62, 133.79, 134.04, 134.12, 137.33, 137.63, 139.31, 163.31, 171.63. 4b: δ = 31.26, 37.12, 38.94, 74.10, 131.23, 132.58, 133.97, 134.27, 137.46, 137.81, 139.70, 142.05, 164.68, 171.68. 4c: δ = 25.21, 31.34, 33.27, 37.43, 39.00, 67.74, 75.75, 124.66, 125.18, 131.39, 132.69, 133.95, 134.18, 137.74, 137.81, 138.02, 139.28, 162.75, 171.68. 4d: δ = 27.67, 31.30, 37.29, 39.00, 66.53, 78.96, 125.40, 131.17, 132.50, 133.60, 133.88, 136.54, 136.82, 139.35, 163.06, 171.59.

<A NAME="RG24902ST-19B">19b</A> Kaiser E. Colescott RL. Bossinger CD. Cook PI. Anal. Biochem.  1970,  34:  595 

<A NAME="RG24902ST-20">20</A>

General Procedure for the Asymmetric Wacker-Type Cyclization of 1: A mixture of immobilized catalyst (0.02 mmol Pd), 2-(2,3-dimethyl-2-butenyl)-phenol(1) (0.2 mmol, 35.2 mg), benzoquinone (0.8 mmol, 86.4 mg) and MeOH (1 mL) was agitated at 60 °C with shaking for 20 h. After being cooled to r.t., the resin was filtered off and washed twice with MeOH (1 mL). The solvent was removed in vacuo and the residue was purified by column chromatography using silica gel and n-hexane-EtOAc (95:5) giving (S)-2-iso-propenyl-2-methyl-2,3-dihydrobenzofuran(2) as colorless oil. The ee was determined by GC (chiral stationary phase capillary column Cyclodex CB).

For recent examples of PEG-supported binaphthyl-based chiral catalysts, see:

<A NAME="RG24902ST-21A">21a</A> Guerreiro P. Ratovelomanana-Vidal V. Genet J.-P. Dellis P. Tetrahedron Lett.  2001,  42:  3423 

<A NAME="RG24902ST-21B">21b</A> Fan Q.-H. Deng G.-J. Lin C.-C. Chan ASC. Tetrahedron: Asymmetry  2001,  12:  1241 

<A NAME="RG24902ST-21C">21c</A> Yang X.-W. Sheng J.-H. Da C S. Wang H.-S. Su W. Wang R. Chan ASC. J. Org. Chem.  2000,  65:  295 

<A NAME="RG24902ST-21D">21d</A> Fan Q.-H. Deng G.-J. Chen X.-M. Xie W.-C. Jiang D.-Z. Liu D.-S. Chan ASC. J. Mol. Cat. A.  2000,  159:  37 ; see also ref. 2b

For recent examples of PEG-supported chiral oxazoline ligands, see:

<A NAME="RG24902ST-22A">22a</A> Annunziata R. Benaglia M. Cinquini M. Cozzi F. Pitillo M. J. Org. Chem.  2001,  66:  3160 

<A NAME="RG24902ST-22B">22b</A> Glos M. Reiser O. Org. Lett.  2000,  2:  2045