Methylenation Diiodomethane-Zinc-Titanium

Diiodomethane-Zinc-Titanium(IV) isopropoxide, 115 Iodomethyltrimethylsilane, 315 Tributyl(iodomethyl)tin, 314 a-METHYLENE-y-BUTYROLACTONES (see Un-saturated Lactones)... 

It is possible to exclusively methylenate a ketone in the presence of an aldehyde by precomplexing the aldehyde (e.g. 76) with Ti(NEt2)4, followed by treatment with the usual methylene zinc/TiCU reagent (equation 17). Takai also studied the chemoselective methylenadon of aldehydes (78) in the presence of ketones, and found the use of diiodomethane, zinc and titanium isopropoxide or trimethylaluminum to be effective (equation 18). ... 

An equimolar mixture of 4 and jS-TiCh generated reactive spedes for the methylenation, as shown in Table 5.2. As described above, the methylenation procedure due to Takai or Lombardo employed diiodomethane, zinc, and titanium(IV) chloride. In these procedures, the titanium(IV) chloride would be reduced to titanium(O), titanium(I), titanium(II), or titanium(III). The oxidation state of tita-... 

Nozaki, Oshima, and Takai reported in 1978 that the reagent prepared from diio-domethane, zinc, and titanium(IV) chloride was effective for the methylenation of ketones [12]. In this procedure, a reagent was prepared by mixing diiodomethane (3.0 equiv.), zinc dust (9.0 equiv.), and titanium(IV) chloride (1.0 equiv.) in THF for 30 min at 25 °C. The ketone substrate (1.0 equiv.) was then added to the prepared reagent. Other metal halides were also examined (Scheme 5.5), but none of them gave better results than titanium) IV) chloride. 

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