Diiodomethane-Zinc-Titanium(IV) Chloride


[75-11-6]  · CH2I2  · Diiodomethane-Zinc-Titanium(IV) Chloride  · (MW 267.84) (Zn)

[7440-66-6]  · Zn  · Diiodomethane-Zinc-Titanium(IV) Chloride  · (MW 65.37) (TiCl4)

[7550-45-0]  · Cl4Ti  · Diiodomethane-Zinc-Titanium(IV) Chloride  · (MW 189.71) (Ti(O-i-Pr)4)

[546-68-9]  · C12H28O4Ti  · Diiodomethane-Zinc-Titanium Tetraisopropoxide  · (MW 284.26)

(reagent combination for methylenation of aldehydes and ketones)

Physical Data: CH2I2: mp 6 °C; bp 181 °C; d 3.325 g cm-3. Zn: mp 419.5 °C; d 7.140 g cm-3. TiCl4: mp -24 °C; bp 136.4 °C; d 1.730 g cm-3. Ti(O-i-Pr)4: mp 20 °C; bp 58 °C/1 mmHg; d 0.955 g cm-3.

Solubility: sol THF.

Preparative Methods: prepared in situ.

Handling, Storage, and Precautions: CH2I2 is corrosive and is light sensitive; it is usually stabilized with a small amount of copper. TiCl4 is highly toxic and extremely moisture sensitive. Ti(O-i-Pr)4 is an irritant and is flammable. Zn is a moisture-sensitive, flammable solid.

General Discussion.

The reagent prepared by the combination of Diiodomethane, Zinc, and Titanium(IV) Chloride is very effective at converting enolizable aldehydes and ketones into their methylene derivatives (eq 1).1 The reaction many times provides improved yields over the conventional Methylenetriphenylphosphorane. The b-acetoxy ketone was transformed into the alkene (eq 1) in 73% yield with minimal side reactions. The standard Wittig conditions produced only a 39% yield of the desired methylenated product along with a number of other side products derived from elimination reactions.2

In the case of a-tetralone, the CH2I2 reagent combination was superior to the Dibromomethane-Zinc-Titanium(IV) Chloride reagent. The former conditions deliver the product in 88% yield, while the latter set produces only an 11% yield of alkene (eq 2).2

By the appropriate choice of reaction conditions, chemoselective methylenations can be performed. One can chemoselectively convert an aldehyde into the methylene derivative in the presence of a ketone (eq 3). This requires that the reagent's reactivity be moderated slightly by using Titanium Tetraisopropoxide in place of TiCl4. The reagent prepared from TiCl4 is too reactive to offer any appreciable levels of selectivity. Alternatively, a ketone may be methylenated selectively in the presence of an aldehyde if the keto-aldehyde is first pretreated with Titanium Tetrakis(diethylamide) (eq 4). The ketones still require the TiCl4 prepared reagent.3

A number of optically active a-amino ketones have been converted to allylic amines using this reagent (eq 5). The yields were moderate and the enantiomeric excesses generally were very high (>98%). The one exception was the a-phenylglycine-derived ketone which provided the alkene in only 48% ee.4

1. Takai, K.; Hotta, Y.; Oshima, K.; Nozaki, H. BCJ 1980, 53, 1698.
2. Hibino, J.; Okazoe, T.; Takai, K.; Nozaki, H. TL 1985, 26, 5579.
3. Okazoe, T.; Hibino, J.; Takai, K.; Nozaki, H. TL 1985, 26, 5581.
4. Burgess, K.; Ohlmeyer, M. J. JOC 1991, 56, 1027.

Michael J. Taschner

The University of Akron, OH, USA

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