J . Am. Chem. SOC.1986, 108, 3145-3155
3145
Trichlorotitanium and Alkoxytitanium Homoenolates. Preparation, Characterization, and Utilization for Organic Synthesis Eiichi Nakamura,* Hiroji Oshino, and Isao Kuwajima* Contribution from the Department of Chemistry, Tokyo Institute of Technology, Meguro, Tokyo 152, Japan. Received September 5, I985
Abstract: The reaction of I-alkoxy- I-siloxycyclopropanes (e.g., 4, 10, 11) with TiC14 gives deep purple, crystalline 3-trichlorotitanium propionates (e.g., 5, 12) in good yield. These compounds are highly thermally stable due to the five-membered chelate structure, which has been elucidated by spectral studies. An alkoxytitanium species generated by treatment of 5 with half an equivalent of a tetraalkoxytitanium is more reactive than 5, providing efficient synthetic routes to 4-hydroxy esters (homcFReformatsky reaction), y-lactones, and cyclopropanecarboxylates The mechanisms of the homoenolateformation reactions are discussed.
The value of enolate anion 1, one of the most important reactive species in organic chemistry, stems mainly from its amphoteric nature (eq I). In this same sense, homoenolate' 2 has at least an equal potentiality but has not received due attention thus far. One of the reasons for the lack of interest in the past2 is that the reactive homoenolate anions (e.g., 2: M = Na, Li)3.4spontaneously cyclize to cyclopropane tautomer 3, which then reacts as a simple alkoxide toward various electrophiles.* The previous chemistry of the homoenolate has therefore been centered only on the least reactive of the class, e.g., M = HgSand Sn.6 Lack of a reasonably general preparative method was another factor which impeded the studies about homoenolate chemistry. Action of a base upon a carbonyl compound generates an enolate anion but does not generate its homologue, since the carbonyl group lowers the pKa value of the /3-hydrogen only very slightly.2
Scheme I G i . 3
0 CI3Ti
