Schrock s catalyst

The following steps are performed in an argon atmosphere glovebox. In a 50-mL round-bottom flask equipped with a Teflon magnetic stirbar, 2.03 g (14.7 mmol) of previously distilled and degassed 1,9-decadiene (9) (Aldrich) and 27.6 mg (3.61 x 10 2 mmol) of Schrock s catalyst (14) (400 1) are combined. In a matter of seconds, the catalyst is dissolved into the monomer and a vigorous evolution of ethylene is observed. The flask is sealed with a Teflon vacuum adapter and removed from the box. The polymerization vessel is immediately connected to the vacuum line, placed into an oil bath, and stirred at 30°C. Intermittent vacuum... 

The molybdenum analogue of this tungsten catalyst is known as Schrock s catalyst [19]. It is less active than its tungsten counterpart, but it is much more resistant to polar groups in the substrate. 

It is worth noting that 6,7-dihydro-2(3//)-oxepinone is an unusual lactone because it can be polymerized by two distinct mechanisms ROP of the cyclic esters by aluminum alkoxides, and the ring-opening metathesis polymerization (ROMP) of endocyclic olefins by the Schrock s catalyst (Fig. 28) [121]. 

Acyclic diene metathesis (ADMET) polymerization of divinyl benzene, shown in Scheme 37, using an extremely reactive tungsten alkylidene catalyst (Schrock s catalyst) yielded PPV oligomers with DP of 8 [153]. In this example ethylene is formed as a side product of metathesis, and its removal by the use of high vacuum helps drive the polymerization in the forward direction. 

Motivated by the potential of fructose analogues as useful pharmacophores en route to allosteric modulators of phosphofructokinase-2 enzymes, Al-Abed and Seepersaud [14e] recently devised a practical, concise approach to carbafructose 64, relying on a ring closing metathesis reaction governed by Schrock s catalyst (Scheme 10). Moving from unsaturated ketose 65, easily obtained from 2,3,5-tri-O-... 

Nugent s catalyst, however, failed to effect the cyclization of the aminodiene 106, that was cyclized to the pyrroline 107 either by Grubbs ruthenium alkylidene catalyst, PhCH=Ru(PCy3)2Cl2, in 77% yield or by Schrock s catalyst, PhC(Me)2CH=Mo=N[2,6-(iPr)2C5H3] [OCMe(CF3)2]2 in 60% yield (Equation (123)).149... 

Grubbs catalyst 77% Schrock s catalyst 60% Nugent s catalyst 0%... 

Scheme 5 suggests that every step of the ADMET polymerization cycle is in equilibrium and that, by shifting the relative concentrations of the condensate and polymer, depolymerization would result. In fact it has been shown that various unsaturated polymers can be depolymerized with excess ethylene, as well as substituted ethylenes. These depolymerizations can be done either with the tungsten or the molybdenum versions of Schrock s catalyst. 

Schrock s catalyst Grubbs s catalyst Catalyst in Figure 14-24... 

TBHP yielded an allylic alcohol, which was benzylated to provide 97. This highly functionalized diene underwent RCM with Schrock s catalyst affording cyclopentene 98 in a yield of 91%. Under the action of hydrogen and Pd/C, hnal reduction and debenzylation were performed simultaneously to give 5a-carba-(3-D-fmctofuranose [54]. 

A.B. Smith and co-workers have devised an efficient strategy for the synthesis of the cylindrocyclophane family of natural products. Olefin ring-closing metathesis was used for the assembly of the [7,7]-paracyclophane skeleton. During their investigations they discovered a remarkably efficient CM dimerization process, that culminated in the total synthesis of both (-)-cylindrocyclophane A and (-)-cylindrocyclophane F. They established that the cross metathesis dimerization process selectively led to the thermodynamically most stable member of a set of structurally related isomers. Out of three commonly used ROM catalysts, Schrock s catalyst proved to be the most efficient for this transformation. 

In this context Schrock s catalyst 84 has been used, too, for olefin RCM and CM reactions in [bmim][PF6] as solvent. Several reactions approached 100% conversion with 5 mol.% of catalyst at 75 °C, using molecules containing various functional groups (Scheme 1.49). A new method to extract small amounts of organic products from IL by carrying out a Soxhlet extraction using PDMS (polydimethyl siloxane) thimbles has also been reported. 

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