Grubbs carbene

Note added in proof For an improved procedure for the preparation of Grubbs carbenes see Wolf J, Stiier W, Griinwald C, Werner H, Schwab P, Schulz M (1998) Angew Chem 110 1165 Angew Chem Int Ed Engl 37 1124... 

Exposure of a monosubstituted allene to a Grubbs carbene complex allows the formation of a 1,3-disubstituted allene accompanied with polymers (Scheme 16.93) [99]. The product distribution depends considerably on the alkyl substituents on the allene moiety and particularly the reaction of a series of phenylallenes undergoes complete conversion to polymers. 

RCM was also employed as a key design element for the synthesis of tricolorin A (106). This novel strategy demonstrated the efficiency of macrocyclizations using the standard ruthenimum catalysis either by the classical Grubbs carbene complex or the recently developed cationic ruthenium aUenylidene complex as the... 

Treatment of enynes 35 and 36 with first generation Grubbs carbene under the above diene ring-closing metathesis conditions did not furnish the desired spiro-cycles. Next, trials of cyclization were attempted by using its imidazolidinylidene... 

Isoxazolo[2,3-a]pyridin-7-ones were prepared by domino metathesis of the strained nitroso Diels-Alder adduct 87 and a terminal alkene in the presence of a catalytic amount of second generation Grubbs carbene or Hoveyda-Grabbs carbene complex. For example, 88 was obtained as the major product along with minor amounts of 89 starting from 87 and but-3-en-l-ol <07OL1485>. 

Grubbs carbene, Cl2(Cy3P)2Ru = CHPh, to give medium-sized rings fused to bis-... 

Another comparative study of the CM reaction catalyzed by a second generation Grubbs carbene complex (without imidazolium tag) has been recently presented by Tang and coworkers [264]. They compared the catalytic transformation of styrene in [BMIM][BF4] and [BMIM PFs] with the same reaction in CH2Q2 (3 h, 45 °C) and obtained comparable yields of the CM product in all solvents in the first cycle. In the case of the two ionic liquids the product was extracted with diethyl ether and the remaining ionic catalyst solution could be recycled four times with only a small drop in catalytic activity (product yield 75% in the fourth cycle compared to 85% in the first cycle in [BMIMjfPFs]). The scope of the study also included the successful... 

A tandem Grubbs carbene/RuCl3 combination was also used for the formation of pyrroles (e.g., 9 10) (Scheme 2(a)). However, the basicity of ni-... 

Basset carbene. In a first step, we studied more extensively the Grubbs carbene 1, as it is now widely used in organic synthesis (see for example [8] and [9] and references therein). 

Scheme 3. Initiation period in the metathesis reaction by the Grubbs carbene 1...

Figure 1. Catalytic activity of the Grubbs carbene 1 in the metathesis reaction of cw-pent-2-ene. Conversion as a function of time at different temperatures.

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