Polymer-Supported β-Amino Thioesters as Catalysts for the Enantioselective Addition of Diethylzinc to Aldehydes

Abstract

A series of novel polymer-supported thioesters were prepared and found to be effective catalysts for the enantioselective addition of diethylzinc to benzaldehyde. These catalysts gave 1-phenylpropanol in up to 86% ee. The catalysts were fully recyclable and could be used in subsequent additions with retention of the enantioselectivity and efficiency levels.

asymmetric catalysis - ligands - nucleophilic additions - polymers - supported catalysis

References

1

Present address: Departamento de Química y Biología, Universidad del Norte, Km 5 via Puerto Colombia, Barranquilla, Colombia.

2 For reviews see: Pu L. Hong-Bin Y. Chem. Rev.  2001,  101:  757 

For reviews of soluble enantioselective catalysts see:

3a Soai K. Shibata T. In Comprehensive Asymmetric Catalysis   Vol. 2:  Jacobsen EN. Pfalz A. Yamamoto H. Springer-Verlag; Berlin: 1999.  p.911-922  

3b Noyori R. In Asymmetric Catalysis in Organic Synthesis   Wiley; New York: 1994.  p.260-278  

3c Soai K. Niwa S. Chem. Rev.  1992,  92:  833 

3d Noyori R. Kitamura M. Angew. Chem., Int. Ed. Engl.  1991,  30:  46 

For reviews of polymer-supported catalysts see:

4a Fan Q.-H. Li Y.-M. Chan ASC. Chem. Rev.  2002,  102:  3385 

4b de Miguel YR. Brulé E. Margue RG. J. Chem. Soc., Perkin Trans. 1  2001,  3085 

4c Clapham B. Reger TS. Janda KD. Tetrahedron  2001,  57:  4637 

5a Hof RP. Poelert MA. Peper NCMW. Kellogg RM. Tetrahedron: Asymmetry  1994,  5:  31 

5b Fitzpatrick K. Hulst R. Kellogg RM. Tetrahedron: Asymmetry  1995,  6:  1861 

5c Kang J. Lee DJW. Kim JI. Chem. Commun.  1994,  2009 

5d Kang J. Kim DS. Kim JI. Synlett  1994,  842 

5e Masaki Y. Satoh Y. Makihara T. Shi M. Chem. Pharm. Bull.  1996,  44:  454 

5f Gibson CL. Chem. Commun.  1996,  645 

5g Kang J. Kim JB. Kim JW. Lee D. J. Chem Soc., Perkin Trans. 2  1997,  189 

5h Nakano H. Kumagai N. Matsuzaki H. Kabuto C. Hongo H. Tetrahedron: Asymmetry  1997,  8:  1391 

5i Iwasa K. Hongo H. Heterocycles  1997,  46:  267 

5j Chelucci G. Berta D. Fabbri D. Pinna GA. Saba A. Ulgheri F. Tetrahedron: Asymmetry  1998,  9:  1933 

5k Aurich HG. Soeberdt M. Tetrahedron Lett.  1998,  39:  2553 

5l Kossenjans M. Soebert M. Wallbaum S. Harms K. Martens J. Aurich HG. J. Chem Soc., Perkin Trans. 1  1999,  2353 

5m Tseng S.-L. Yang T.-K. Tetrahedron: Asymmetry  2004,  15:  3375 

For recent examples of b-amino sulfur ligands as catalysts in the diethylzinc addition to aldehydes see:

6a Braga AL. Milani P. Paixão MW. Zeni G. Rodrigues OED. Alves EF. Chem. Commun.  2004,  2488 

6b Braga AL. Vargas F. Silveira CC. de Andrade LH. Tetrahedron Lett.  2002,  43:  2335 

6c Braga AL. Appelt HR. Schneider PH. Rodrigues OED. Silveira CC. Wessjohann LA. Tetrahedron  2001,  57:  3291 

6d Jimeno C. Moyano A. Pericàs MA. Riera A. Synlett  2001,  1152 

7 For examples of the lower catalytic effectiveness of β-amino thioethers over the corresponding disulfides see: Braga AL. Appelt HR. Schneider PH. Silveira CC. Wessjohann LA. Tetrahedron: Asymmetry  1999,  10:  1733 

8a In related amino aryl diselenides, Wirth et al. have unequivocally established that an ethyl selenide (45% yield) is obtained upon treatment with diethylzinc. This ethyl selenide was proven not to be the dominant catalytically active species in the addition of diethylzinc to benzaldehyde (17% yield). Furthermore, these workers also provided NMR evidence for zinc selenolate dimers. See: Wirth T. Kulicke KJ. Fragale G. Helv. Chim. Acta  1996,  79:  1957 

8b A similar observation has been made that selenoethers derived from aliphatic amino diselenides are not catalytically productive: Braga AL. Paixão MW. Lüdtke DS. Silveira CC. Rodrigues OED. Org. Lett.  2003,  5:  2635 

9 Gibson CL. Tetrahedron: Asymmetry  1999,  10:  1551 

10 Kleijn H. Rijnberg E. Jastrzebski JTBH. van Koten G. Org. Lett.  1999,  1:  853 

11 Lui G. Ellman JA. J. Org. Chem.  1995,  60:  7712 

12 Hanessian S. Xie F. Tetrahedron Lett.  1998,  39:  733 

13 Hanessian S. Huynh HK. Tetrahedron Lett.  1999,  40:  671 

14 Lecavalier P. Bald E. Jiang Y. Fréchet JMJ. Reactive Polymers  1985,  3:  315 

15

Typical Procedure for the Synthesis of the Polymer-Supported Thioesters 6 and 7.
To a stirred solution of [(2S)-1-(polystyrylmethyl)pyrrol-idinyl]methanol (0.5008 g) and triphenylphosphine (0.5885 g) in anhyd toluene (10 mL) under nitrogen was added at r.t. a solution of DEAD (0.3912 g) in toluene (1 mL). After 3-5 min thiobenzoic acid (0.3012 g) in toluene (1 mL) was added. The resulting mixture was stirred for a further 45 h at r.t. At the completion of this period the polymer was filtered and rinsed with toluene, DMF and EtOH. The polymer beads were then transferred to a soxhlet apparatus and washed with THF for 1 d, rinsed with acetone and finally soxhlet extracted with Et₂O for 1 d. The beads were then dried in a drying pistol (40 °C, 0.05 mmHg) for 24 h to give 0.5639 g of polymer. IR (KBr): ν_max = 1664 cm^-1. Anal. Calcd: N, 2.08; S, 4.78. Found: N, 1.94; S, 3.82. Loading 1.19 mmol S/g and an 80% conversion based on sulfur microanalysis.

16 Yelm KE. Tetrahedron Lett.  1999,  40:  1101 

17 Govindachari TR. Rajagopalan TG. Viswanathan N. J. Chem. Soc., Perkin Trans. 1  1974,  1161 

18

Typical Procedure for the Enantioselective Addition of Diethylzinc to Benzaldehyde Catalysed by Polymer-Supported Catalysts 6-8.
Diethylzinc (1.87 mL of a 1 M solution in hexane, 1.87 mmol) was added to a stirred solution of the catalyst (0.024 mmol, 0.048 mmol, or 0.096 mmol based on sulfur content) in anhyd toluene (5 mL) under a nitrogen atmosphere. After stirring at r.t. for 2 h the solution was cooled to -27 °C whereupon, freshly distilled benzaldehyde (0.937 mmol) was added and the resulting solution was stirred at 0 °C. After stirring for 19 h at this temperature additional diethylzinc was added (1.87 mL, 1.87 mmol) and the mixture stirred for a further 46 h at 0 °C. At the completion of this period there was no starting aldehyde, so HCl was added (1 M, 3 mL). The aqueous phase was extracted with CH₂Cl₂ (3 × 10 mL) and dried over Na₂SO₄. Evaporation of the solvent and silica column chromatography (hexane-EtOAc, 88:12) afforded (R)-(+)-1-phenyl-1-propanol as a colourless oil. ¹H NMR (CDCl₃): δ = 0.9 (t, 3 H, CH₂CH ₃, J = 7.4 Hz), 1.65-2.00 (m, 3 H, CH ₂CH₃, J = 7.4 Hz, OH), 4.60 (t, 1 H, CHOH, J = 6.6 Hz), 7.30-7.40 (m, 5 H, ArCH). The ee was determined by HPLC using a DAICEL chiralcel OB column with 3% i-PrOH in hexane (flowrate: 0.5 mL/min); t _R = 25 min for the S-isomer and 31 min for the R-isomer.

19 Itsuno S. Fréchet JMJ. J. Org. Chem.  1987,  52:  4140 

20 Sung DW. Hodge P. Stratford PW. J. Chem. Soc., Perkin Trans. 1  1999,  1463