Structural elucidation of a methylenation reagent of esters: synthesis and reactivity of a dinuclear titanium(iii) methylene complex.

Takashi Kurogi,Kazuhiko Takai,Kaito Kuroki,Shunsuke Moritani

doi:10.1039/d0sc06366e

Takashi Kurogi, Kazuhiko Takai + Show 2 more

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https://doi.org/10.1039/d0sc06366e

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Abstract

Transmetallation of a zinc methylene complex [ZnI(tmeda)]2(μ-CH2) with a titanium(iii) chloride [TiCl3(tmeda)(thf)] produced a titanium methylene complex. The X-ray diffraction study displayed a dinuclear methylene structure [TiCl(tmeda)]2(μ-CH2)(μ-Cl)2. Treatment of an ester with the titanium methylene complex resulted in methylenation of the ester carbonyl to form a vinyl ether. The titanium methylene complex also reacted with a terminal olefin, resulting in olefin-metathesis and olefin-homologation. Cyclopropanation by methylene transfer from the titanium methylene proceeded by use of a 1,3-diene. The mechanistic study of the cyclopropanation reaction by the density functional theory calculations was also reported.

Highlights

Since the rst report of the Tebbe reagent in 1978,1,2 titanium methylene species[3] have been widely investigated and utilized for Wittig-type ole nation of carbonyls,1,3b,3c,4 C–H activation,[5] ole n homologation,[1] ole n metathesis[6] and ring-opening metathesis polymerization.[7]
The titanium methylene complex reacted with a terminal olefin, resulting in olefin-metathesis and olefinhomologation
The rst key step in preparing the CH2X2–Zn(Pb)–TiCl4 methylenation reagent involves reductive cleavage of C–X bonds by Zn(0) to form a zinc methylene species “CH2(ZnX)2”,11,17 which was trapped as CH2(SnMe3)[2] upon treatment with ClSnMe3 (Scheme 1b).8,16a The second reductive cleavage of a C–X bond by Zn(0) to give the zinc methylene “CH2(ZnI)2” is accelerated via transmetallation with a catalytic amount of a lead(II) salt

Summary

Introduction

Since the rst report of the Tebbe reagent in 1978,1,2 titanium methylene species[3] have been widely investigated and utilized for Wittig-type ole nation of carbonyls,1,3b,3c,4 C–H activation,[5] ole n homologation,[1] ole n metathesis[6] and ring-opening metathesis polymerization.[7]. Edge Article place to generate a titanium(III) methylidene species [(L)nTi(1⁄4CH2)Cl] due to its powerful methylenation reactivity.[12,13] To clarify the reactive species in the methylenation reagent, we have recently synthesized and isolated the zinc methylene “CH2(ZnX)2” as a dinuclear zinc m-methylene complex, namely [ZnI(L)n]2(m-CH2) (1a: L 1⁄4 tmeda, n 1⁄4 1; 1b: L 1⁄4 2,6-lutidine, n 1⁄4 2), and methylenation of ester carbonyls proceeded by mixing 1a and [TiCl3(tmeda)(thf)] (2).[20] we report a structural characterization of a titanium methylene complex formed by transmetallation between the zinc methylene and titanium(III) chloride as well as methylene transfer reactions to ether carbonyls and ole ns.

Results

Conclusion