Diethylaluminum 2,2,6,6-Tetramethylpiperidide

[54159-47-6]  · C13H28AlN  · Diethylaluminum 2,2,6,6-Tetramethylpiperidide  · (MW 225.35)

(combined Lewis acid-base reagent for oxygen-containing functional groups; can isomerize epoxides1 and oxetanes;3 can function as a base;4 can enolize meso-cyclic acetals5)

Alternate Name: DATMP.

Solubility: sol benzene, toluene, hexane, CH2Cl2.

Form Supplied in: prepared and used in situ.

Preparative Method: prepared in situ from Diethylaluminum Chloride and Lithium 2,2,6,6-Tetramethylpiperidide in benzene at 0 °C.1

Handling, Storage, and Precautions: the dry solid and solutions are highly flammable and must be handled in the absence of oxygen and moisture. Use in a fume hood.

Isomerization of Epoxides to Allylic Alcohols.

This reaction is usually carried out with a lithium dialkylamide base (see Lithium Diethylamide). However, organoaluminum amides of the type Et2AlNR1R2 are also highly effective because of the high affinity of aluminum for oxygen. Among various organoaluminum amides, DATMP is the most satisfactory with respect to reactivity and selectivity.1 The reagent effects the isomerization of (E)-cyclododecene oxide to (E)-2-cyclododecen-1-ol in 99% yield under very mild conditions (eq 1). The effectiveness of DATMP is clearly demonstrated by comparison with other organoaluminum amides in the conversion of (E)-cyclododecene oxide to (E)-2-cyclododecen-1-ol in benzene at 0 °C for 1 h: Et2AlN(i-Pr)2, 65%; Et2AlNCy2, 36%; Et2AlNEt2, 5%; i-Bu2AlNPh2, 48%; i-Bu2AlNMePh, 69%; i-Bu2AlN(i-Pr)2, 30%. 6,7-Epoxygeraniol and squalene terminal epoxide give (E)-3,7-dimethyl-2,7-octadiene-1,6-diol and (6E,10E,14E,18E)-2,6,10,15,19,23-hexamethyl-1,6,10,14,18,22-tetracosahexaen-3-ol, respectively, in high yields under very mild conditions (eqs 2 and 3). Notably, no cyclized byproducts are observed in these two cases. Unfortunately, the oxides of cyclopentene, cyclohexene, and cycloheptene are stable under similar reaction conditions.

DATMP enables the regioselective isomerization of trisubstituted epoxides. Thus (Z)-6-methyl-5-undecene oxide is converted to the disubstituted allylic alcohol in high yield, while its (E)-isomer is transformed mainly into the trisubstituted allylic alcohol (eqs 4 and 5).1 The bulk of the amide base may play a significant role in determining the course of the isomerization.

The remarkable selectivity inherent in DATMP is further demonstrated by the selective transformation of diepoxyfarnesol. Thus diepoxyfarnesol gives (E)-3,11-dimethyl-7-methylene-2,11-dodecadiene-1,6,10-triol upon exposure to lithium diethylamide, while treatment of the diepoxide with DATMP affords (2E,7E)-3,7,11-trimethyl-2,7,11-dodecatriene-1,6,10-triol as the sole isolable product (eq 6).

1,3-Diene Synthesis.

DATMP has been applied to a 1,3-diene synthesis which involves: (1) epoxidation of an allylic alcohol with t-Butyl Hydroperoxide in the presence of a vanadium catalyst followed by trimethylsilylation; (2) selective epoxide opening by means of DATMP and subsequent desilylation, producing a 3-ene-1,2-diol; and (3) removal of both hydroxy groups through bromination with a mixture of Phosphorus(III) Bromide and Copper(I) Bromide followed by Zinc debromination.2 The reaction sequence has been used for the synthesis of b-myrcene from nerol, trans-b-ocimene from geraniol, and a- and b-farnesenes from their biological precursors (eqs 7 and 8). A C12 sex pheromone of red bollworm moth has been prepared efficiently using this methodology.

Conversion of Oxetanes to Homoallylic Alcohols.

Oxetanes can also be cleaved by organoaluminum amides, particularly by diethylaluminum methylanilide, providing (E)-homoallylic alcohols (eqs 9 and 10).3 A higher reaction temperature and a longer reaction time are required compared to the epoxide cleavage. With this methodology, a fundamental medium ring sesquiterpene, humulene, has been synthesized in a highly stereoselective manner (eq 11).

Aluminum Enolates.

Organoaluminum enolates are conveniently prepared from carbonyl substrates such as ketones and t-butyl acetate using DATMP as the base. Subsequent addition of aldehydes and ketones affords the desired aldol adducts in good yields (eqs 12 and 13).4

Asymmetric enolization of meso-cyclic acetals of (2R,4R)-pentanediol is effected with a series of trialkylaluminums and organoaluminum amides (eq 14).5 Among a series of organoaluminum amides, diisobutylaluminum t-butyl(t-butylcyclohexylmethyl)amide is most effective for this transformation.

Polymerization.

The DATMP reagent can be used as a polymerization catalyst for ethylene and propylene.6


1. (a) Yasuda, A.; Tanaka, S.; Oshima, K.; Yamamoto, H.; Nozaki, H. JACS 1974, 96, 6513. (b) Yasuda, A.; Yamamoto, H.; Nozaki, H. BCJ 1979, 52, 1705.
2. (a) Tanaka, S.; Yasuda, A.; Yamamoto, H.; Nozaki, H. JACS 1975, 97, 3252. (b) Yasuda, A.; Tanaka, S.; Yamamoto, H.; Nozaki, H. BCJ 1979, 52, 1752.
3. Kitagawa, Y.; Itoh, A.; Hashimoto, S.; Yamamoto, H.; Nozaki, H. JACS 1977, 99, 3864.
4. Nozaki, H.; Oshima, K.; Takai, K.; Ozawa, S. CL 1979, 379.
5. Naruse, Y.; Yamamoto, H. T 1988, 44, 6021.
6. Langer, A. W.; Burkhardt, T. J.; Steger, J. J. Polym. Sci. Technol. 1983, 225.

Keiji Maruoka & Hisashi Yamamoto

Nagoya University, Japan



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