Grubbs number

Further detailed investigations towards new chiral ruthenium catalysts that could enhance enantioselectivity and expand the substrate scope in asymmetric RCM were reported by Grubbs and co-workers in 2006 [70] (Fig. 3.24). Catalysts 59 and 61, which are close derivatives of 56 incorporating additional substituents on the aryl ring para to the ort/to-isopropyl group, maintained similar enantioselectivity than 56b. However, incorporation of an isopropyl group on the side chain ortho to the ortho-isopropyl group 60 led to an increase in enantioselectivity for a number of substrates. 

There are a number of reports of NHC complexes of mid-late transition metals being used as catalysts for atom transfer radical polymerisation (ATRP) of acrylates and styrene. Grubbs reported Fe(II) complexes of a simple monodentate carbene. 

The main reason for the rapid development of metathesis reactions on a laboratory scale (the reaction itself had been known for quite a long time) has been the development of active and robust second-generation ruthenium catalysts (6/3-14 to 6/3-16), which usually provide better yields than the first-generation Grubbs catalysts (6/3-9 or 6/3-13) (Scheme 6/3.2). This also reflects the huge number of domino processes based on ruthenium-catalyzed metathesis, which is usually followed by a second or even a third metathesis reaction. However, examples also exist where, after a metathesis, a second transition metal-catalyzed transformation or a pericyclic reaction takes place. 

The synthesis of the /V-protected 7-methylazepine derivative 34 was achieved in 89% yield by a ring-closing metathesis reaction on 33 mediated by Grubbs I ruthenium catalyst. This azepine was an important precursor for the preparation, via epoxidation of the double bond, of a number of 7-methylazepanone derivatives for evaluation as cathepsin K inhibitors <06JMC1597>. 

The chemistry described in this review article demonstrates the impressive positive influence that catalytic RCM has had on our research in connection to the development of other catalytic and enantioselective C-C bond forming reactions. There is no doubt that in the absence of pioneering work by Schrock and Grubbs, the Zr-catalyzed alkylation and kinetic resolution would be of less utility in synthesis. The number of unsaturated heterocyclic and carbocyclic substrates available for Zr-catalyzed asymmetric carbomagnesation would be far more limited without catalytic RCM. 

The critical value from Table Al is 42.8 and therefore Laboratory 5 s data is removed. Note that this is allowed because the number of laboratories removed so far does not exceed 2/9th. In a similar manner, the Grubbs statistics are recalculated for this second cycle for the remaining 19 laboratories. 

In 1992, Grubbs and coworkers published the synthesis of a new family of me-tallocarbenes and developed their use as catalysts for ring-closing metathesis (RCM) reactions [103-105], Gradually, these compounds were used by a large number of research groups [106-108], because their utilization was close to ideal... 

Grubbs and co-workers have recently reported a new class of Ru catalysts (83, Eq 2) [29] that bear a chiral monodentate N-heterocyclic carbene ligand [30]. The reactions illustrated in Eq 2 include the highest ee reported (13-90% ee) asymmetric induction is clearly dependent on the degree of olefin substitution (cf. Schemes 18 and 4 for comparison with the Mo-catalyzed reactions of the same substrates). As is the case with nearly catalytic enantioselective reactions [4], the identity of the optimal catalyst depends on the substrate a number of chiral... 

Some other natural compounds have been transformed for their use in the synthesis of polymers via olefin metathesis processes. As mentioned in the introduction, furans, which are obtained from carbohydrates, are perfect precursors of monomers for ROMP via simple Diels-Alder cycloadditions (n) (Scheme 25) [26]. In this regard, the first example of the ROMP of 7-oxabicyclo[2.2.1]hept-5-ene derivatives was reported by Novak and Grubbs in 1988 using ruthenium- and osmium-based catalysts [186]. The number of examples of ROMP with monomers with this generic structure is vast, and it is out of the scope of this chapter to cover all of them. However, it is worth mentioning here the great potential of a renewable platform chemical like furan (and derived compounds), which gives access to such a variety of monomers. 

Because of the small margin of safety, few controlled experimental studies of hydrogen cyanide toxicity have been conducted with human subjects. Barcroft (1931) exposed a man at a nominal concentration of 625 ppm for 1.5 min in an airtight chamber. Five minutes after the start of the experiment, the man developed a momentary feeling of nausea at 10 min, he had difficulty concentrating in a conversation. No toxic effects were observed in several human volunteers (number not reported) exposed at 240 or 360 ppm for 1.5-2 min (Grubbs 1917). 

The [l,6]benzo- and [l,6]pyrido-diazocines 78 were obtained by one-pot procedure via isomerization-RCM of the diene 76 in the presence of the Grubbs second-generation catalyst 77 (Scheme 11) <2004TL9171>. Although the number of literature examples describing isomerization-RCM is still limited, this concept has... 

A number of theoretical studies support the results of the experimental work by Grubbs and Wagener. Chen performed a quantum mechanical/molecular mechanics (QM/MM) study on the olefin mefafhesis reaction comparing (2a) and (4a). The... 

Grubbs and coworkers performed a systematic study on a large number of olefin metathesis initiators that differed only in... 

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