[14405-45-9]  · C15H21InO6  · Tris(acetylacetonato)indium  · (MW 412.18)

(mild Lewis acid used as a cocatalyst to effect carbonyl additions2)

Physical Data: mp 186 °C; 1H NMR (CDCl3) d 2.02 (CH3), 5.41 (CH); d 1.41 g cm-3.

Solubility: readily sol toluene; moderately sol ethanol; almost insol water.

Form Supplied in: white crystalline solid; readily available. Drying: the freshly prepared indium compound can be recrystallized from cold acetone as colorless crystals and sublimed at 260-280 °C.

Handling, Storage, and Precautions: the dry solid can be stored in air. In(acac)3 has a reputed toxicity of LD50: 79 mg kg-1 with TSCA HMIS: 2-1-0-X.

1,2 vs. 1,4 Cycloadditions.

While organoindium compounds have found recent synthetic applications for a number of organic transformations including allylations,3 cyclopropanations,4 Reformatsky,5 and cross-coupling reactions,6 catalysis using indium precursors has been relatively unexplored. A recent study has shown that InCl3 can be employed as a cocatalyst along with Chlorotrimethylsilane for the conversion of O-trimethylsilyl monothioacetals to sulfides.7 In a similar manner, In(acac)3 has been used to control the chemoselectivity in the palladium-catalyzed cycloaddition of carbonyl compounds.2 As expected, addition of trimethylenemethane to enones in the presence of a palladium catalyst affords the 1,4-adduct exclusively.8 However, as little as 10 mol % of In(acac)3 can be utilized as a cocatalyst to alter the reaction course from conjugate to 1,2-addition (eq 1). Increasing reaction temperatures by going from refluxing THF to dioxane increases the ratio of 1,2- vs. 1,4-addition products.

Exocyclic enone derivatives, which are particularily prone to conjugate addition, can be diverted from this pathway to give exclusive formation of the corresponding 1,2-addition products by using an InIII cocatalyst (eq 2). Reactions with carbohydrates bearing several Lewis basic sites also proceed with good 1,2-selectivity and diastereoselectivity in the presence of In(acac)3. Steric hindrance may inhibit 1,2-addition, however, as in the case of galactopyranose (eq 3) which gives predominant formation of the 1,4-adduct (1,2 vs. 1,4 = 1:4.2).

Finally, addition of trimethylenemethane to keto aldehydes affords the corresponding methylenetetrahydrofuran with enhanced diastereoselectivity (>19:1) when compared to reactions employing tin as a cocatalyst (eq 4).9 This overall switch in chemoselectivity using indium complexes promises to be useful for a number of nucleophilic reactions.

1. (a) Morgan, G. T.; Drew, H. D. K. JCS 1921, 1058. (b) Carty, A. J.; Tuck, D. G.; Bullock, E. CJC 1965, 43, 2559. (c) Matsubara, N.; Kuwamoto, T. IC 1985, 24, 2697.
2. Trost, B. M.; Sharma, S.; Schmidt, T. JACS 1992, 114, 7903.
3. (a) Araki, S.; Ito, H.; Butsugan, Y. JOC 1988, 53, 1831. (b) Araki, S.; Ito, H.; Katsumura, N.; Butsugan, Y. JOM 1989, 369, 291. (c) Araki, S.; Katsumura, N.; Ito, H.; Butsugan, Y. TL 1989, 30, 1581. (d) Araki, S.; Shimizu, T.; Johar, P. S.; Jin, S-J.; Butsugan, Y. JOC 1991, 56, 2538. (e) Araki, S.; Katsumura, N.; Butsugan, Y. JOM 1991, 415, 7. (f) Araki, S.; Jin, S-J.; Idou, Y.; Butsugan, Y. BCJ 1992, 65, 1736. (g) Jin, S-J.; Araki, S.; Butsugan, Y. BCJ 1993, 66, 1528. (h) Kim, E.; Gordon, D. M.; Schmid, W.; Whitesides, G. M. JOC 1993, 58, 5500. (i) Beuchet, P.; Le Marrec, N.; Mosset, P. TL 1992, 33, 5959. (j) Li, C. J.; Chan, T. H. TL 1991, 32, 7017. (k) Chan, T. H.; Li, C.-J. CC 1992, 747.
4. Araki, S.; Butsugan, Y. CC 1989, 1286.
5. (a) Araki, S.; Ito, H.; Butsugan, Y. SC 1988, 18, 453. (b) Johar, P. S.; Araki, S.; Butsugan, Y. JCS(P1) 1992, 711.
6. Nomura, R.; Miyazaki, S-I.; Matsuda, H. JACS 1992, 114, 2738.
7. (a) Mukaiyama, T.; Ohno, T.; Nishimura, T.; Han, J. S.; Kobayashi, S. CL 1990, 2239. (b) Mukaiyama, T.; Ohno, T.; Nishimura, T.; Han, J. S.; Kobayashi, S. BCJ 1991, 64, 2524.
8. (a) Trost, B. M.; Chan, D. M. T. JACS 1983, 105, 2315. (b) Trost, B. M.; Chan, D. M. T. JACS 1983, 105, 2326. (c) Trost, B. M.; Miller, M. L. JACS 1988, 110, 3687.
9. (a) Trost, B. M.; King, S. A.; Nanninga, T. N. CL 1987, 15. (b) Trost, B. M.; King, S. A.; Schmidt, T. JACS 1989, 111, 5902. (c) Trost, B. M.; King, S. A. JACS 1990, 112, 408.

Stephen A. Westcott

University of North Carolina, Chapel Hill, NC, USA

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