The First Allylation of Imines with Allyltrichlorosilanes Using Neutral Coordinate-Organocatalysts

Abstract

Imines derived from aldehydes and 2-aminophenols reacted with allyltrichlorosilanes in the presence of DMF, HMPA, or pyridine N-oxide as a neutral coordinate-organocatalyst to afford the corresponding homoallylic amines in high yields with high stereoselectivity; this is the first example of allylation of imines with allyltrichlorosilanes.

allylations - imines - catalysis - neighboring-group effects - stereoselective

References

For recent reviews on allylmetal additions:

1a Puentes CO. Kouznetsov V. J. Heterocycl. Chem.  2002,  39:  595 

1b Denmark SE. Almstead NG. In Modern Carbonyl Chemistry   Otera J. Wiley-VHC; Weinheim: 2000.  Chap. 10.

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We have successfully utilized 2-aminophenols-derived imines for chiral zirconium-catalyzed asymmetric reactions. For leading references, see:

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5

General procedure for allylation: To a solution of imine 3 (0.3 mmol) and 2-methyl-2-butene (0.3 mmol) in DMF (0.3 mL) was added dropwise allylic trichlorosilane 4 or 6 (1.5 equiv) at 0 °C. After stirring vigorously for 5 h at the same temperature, triethylamine (0.2 mL) in methanol (1.0 mL) was added to quench the resulting viscous solution. The mixture was diluted with diethyl ether (40 mL) and water (20 mL). The organic layer was separated, washed twice with water (20 mL), dried over anhydrous Na₂SO₄, filtered, and purified by preparative TLC (hexane/ethyl acetate, 6:1) to give adduct 5 or 7.

6 Porter JR. Traverse JF. Hoveyda AH. Snapper ML. J. Am. Chem. Soc.  2001,  123:  10409 

Phenyliodonium dicarboxylate-mediated intra- and intermolecular carbon-carbon bond-forming reactions of phenols with alkenes were reported, see:

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8

Products 8 were prepared from crotylation of 2-amino-p-cresol/benzaldehyde-imine under the conditions similar to crotylation of 3a (Scheme [1] ). The reactions with (E)- and (Z)-6 at r.t. for 5 h provided syn-8 (74% yield, 86% syn) and anti-8 (76% yield, >99% anti), respectively.

9 Hoffmann RW. Endesfelder A. Liebigs Ann. Chem.  1987,  215