Dichloro[1,2-ethanediylbis(1,2,3,3a,7a-h)-4,5,6,7-tetrahydro-1H-indene-1-ylidene] titanium

[]  · C20H24Cl2Ti  · (383.18)

(used as a source of ‘Cp2TiH’)

Alternate Name: [(EBTHI)TiCl2]1

Physical Data: red solid; mp 256-261°C.

Solubility: THF, diethyl ether, dichloromethane.

Form Supplied in: (EBTHI)TiCl2 is commercially available in the racemic form but can be resolved by using (R)-2,2-binaphth-1,1-diol and p-aminobenzoic acid.2

Handling, Storage, and Precautions: No special handling is required.

Synthesis of Homoallylic Alcohols

The complex (S,S)-dichloro[1,2-ethanediylbis(1,2,3,3a,7a-h)-4,5,6,7-tetrahydro-1H-indene-1-ylidene]titanium [(S,S)-EBTHITiCl2] is a precatalyst for the formation of chiral allyl and crotyl titanium species. Activation of the catalyst with n-propylmagnesium bromide and allyl- or crotylmagnesium bromide followed by treatment with an aldehyde produces homoallylic alcohols in moderate enantioselectivity (eq 1).3 Unfortunately, in the case of the crotyl species, high des are restricted to pivaldehyde and benzaldehyde.

Reduction

In general, the reduction of dialkyl ketones proceeds with poor selectivity. Treatment of (S,S)-EBTHITiCl2 with PhMeSiH2 produces the active catalyst for the reduction of a variety of dialkyl ketones.4 The yields of the reactions are good and the ee's are low to moderate, however the results are similar to other dialkyl ketone reductions in the literature (eq 2).5

Reduction of esters using rac-EBTHITiCl2 to the corresponding alcohols proceeds without opening of an epoxide.6 Imines are reduced with (R,R)-EBTHITiCl2, although the corresponding (R,R,R)-binaphth-1,1-diol complex is more common. This reaction proceeds with good-to-excellent yields and high enantioselectivities.7

Cycloisomerization

Cycloisomerization of 1,6-dienes with rac-EBTHITiCl2 is easily accomplished. Treatment of the diene with EBTHITiCl2 and n-butylmagnesium bromide produces cyclohexenes, whereas the use of Cp2TiCl2 and n-butylmagnesium bromide yields cyclopentenes (eq 3).8


1. Hoveyda, A. H.; Morken, J. P., Angew. Chem., Int. Ed. Engl. 1996, 35, 1263.
2. Chin, B.; Buchwald, S. L., J. Org. Chem. 1996, 61, 5650.
3. Collins, S.; Kuntz, B. A.; Hong, Y., J. Org. Chem. 1989, 54, 4154.
4. Xin, S.; Harrod, J. F., Can. J. Chem. 1995, 73, 999.
5. Ojima, I.; Catalytic Asymmetric Synthesis; VCH Publishing: New York, 1993.
6. Barr, K. J.; Berk, S. C.; Buchwald, S. L., J. Org. Chem. 1994, 59, 4323.
7. Willoughby, C. A.; Buchwald, S. L., J. Am. Chem. Soc. 1994, 116, 8952.
8. Okamoto, S.; Livinghouse, T., Organometallics 2000, 19, 1449.

Erik Kuester

Wayne State University, Detroit, MI, USA



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