reaction smoothly to furnish the corresponding homoallylic amine in
good yield (3o, Table 4). Aromatic amine with electron donating
group also furnished the corresponding homoallylic amine with
slightly lower yield (3p, Table 4). Therefore, not only the electron
withdrawing group on aldehyde portion of aldimines but also the
electron withdrawing group on amine portion enhanced the
electrophilicity of imine carbon to attract the allyl nucleophile from
silane reagent.
corresponding homoallylic amine derivative 7 was successfully
produced in 86% yield, under optimized conditions (Scheme 3).
Scheme 3
Table 4. Allylation of aldimines under optimized conditionsa
3. Conclusions
In conclusion, we have developed a simple protocol for the
allylation of 2-amino phenol derived aldimines with
allyltrichlorosilane. The homoallylic amines were obtained in good
to high yields under thermal conditions. This methodology was
further extended to other direction group containing aldimines such
as salicylaldimines and benzoylhydrazone to generate corresponding
homoallylic amine derivatives. The process has the advantages of
being catalyst and metal free, highly efficient, bench friendly and
environmentally benign. Further investigations to clarify the
mechanism of the reaction are currently underway.
Acknowledgment
We thank DST and CSIR, New Delhi for financial support.
KV thanks UGC, New Delhi for SRF. We gratefully acknowledge
Pondicherry University for NMR/IR data. DST-FIST programme
and UGC-SAP (DSA) awarded to Department of Chemistry,
Pondicherry University are gratefully acknowledged for HRMS.
Supplementary data
Experimental procedures, compound characterization data (1H
&13C NMR, HRMS) for all compounds associated with this article
can be found in the online version.
aReaction
condition:
Aldimine
(1.0
equiv.),
allyltrichlorosilane (1.5 equiv.), toluene (6 mL). bYields
are of isolated products.
References and Notes
The aldimine derivative of benzaldehyde bearing a phenyl
group instead of an ortho-hydroxyphenyl group 4 was also subjected
to react with allyltrichlorosilane at higher temperature, however, no
allylation product was observed (Scheme 2). It was known that the
ortho-hydroxyl group proximal to the imine nitrogen facilitates the
reaction by covalent bond formation with the silicon atom of the
allylating reagent.6,11
1. (a) Wright, D. L.; Schulte II, J. P.; Page, M. A.; Org. Lett. 2000, 2,
1847. (b) Nicolaou, K. C.; Rodriguez, R. M.; Mitchell, H. J.; Suzuki,
H.; Fylaktakidou, K. C.; Baudoin, O.; Delft, F. L. V. Chem. Eur. J.
2000, 6, 3095. (c) Randl, S.; Blechert, S. J. Org. Chem. 2003, 68,
8879. (d) Lee, C.-.L.; Ling, X. Y.; Loh, T. P. J. Org. Chem. 2004, 69,
7787. (e) Xie, W.; Zou, B.; Pei, D.; Ma, D. Org. Lett. 2005, 7, 2775
(f). Kropf, J. E.; Meigh, I. C.; Bebbington, M. W. P.; Weinreb, S. M.
J. Org. Chem. 2006, 71, 2046.
2. For recent reviews on addition of allylmetals to imines and their
analogues,see: (a) Kobayashi, S.; Ishitani, H. Chem. Rev. 1999, 99,
1069. (b) Enders, D.; Reinhold, U. Tetrahedron: Asymmetry 1997, 8,
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ꢀ
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Scheme 2
In addition, it was anticipated that not only 2-aminophenol
derivatives, but also the directing group such as –OH group on
aldehyde portion also displayed similar effect.
Indeed,
9. Dalko, P. I.; Moisan, L. Angew. Chem. Int. Ed. 2004, 43, 5138.
10. Kobayashi, S.; Sugiura, M.; Ogawa, C. Adv. Synth. Catal. 2004, 346,
1023.
salicylaldehyde-derived aldimines were found to react with
allyltrichlorosilane smoothly under the identical condition (Table 4).6
These results indicates that the allylsilane with five coordination
requires elevated temperature to transfer the allyl group from silane
to imine carbon in addition to the requirement of proximal –OH
group.
11. Jagtap, S. B.; Tsogoeva, S. B. Chem. Commun. 2006, 4747.
Further to test the adaptability of this methodology, the
benzoylhydrazone 6 was treated with allyltrichlorosilane and the
3