Robinson’s catalyst

SOLVENT-FREE DEHYDROGENATION OF SECONDARY ALCOHOLS IN THE ABSENCE OF HYDROGEN ACCEPTORS USING ROBINSON S CATALYST... 

In efforts to decarbonylate the allenylaldehyde 87 with Wilkinson s catalyst, Marshall and Robinson observed the formation of the furan 88 rather than the desired hydrocarbon, the allene 89 (Scheme 15.21) [46]. 

D. E. J. E. Robinson, S. D. Bull, Kinetic Resolution Strategies using Non-Enzymatic Catalysts, Tetrahedron Asymmetry 2003, 14, 1407-1446. 

Claisen-Schmidt catalyst, R. Robinson s elegant method for the construction of ring A of steroids is illustrated by the synthesis of the bicyclic diketone (2). A Michael addition of 0.5 mole of 2-methylcyclohexane-l, 3-dione to methyl vinyl ketone under catalysis by methanolic potassium hydroxide gives (1), which is... 

There is less abundant information about HBr and HI, but if we apply Robinson s treatment to the vapour pressure data we find piC(HBr)= -8, pK(Hl)= -9, compared with pR (HCl) = -6, suggesting that the strengths of the three acids are approximately in the ratio 1 10 10. Further, investigations in non-aqueous solvents often show that HBr is a considerably stronger acid than HCl. Thus conductivity measurements in anhydrous acetic acid indicate a ratio of about 20 between the dissociation constants of these two acids, while in acetonitrile we have piC(HBr) = 5.5 and pK(HCl) = 8.9. It is also frequently found that HBr is a much more effective acid catalyst than HCl under conditions where both acids are undissociated. It is of interest that studies... 

In the earliest period of complex natural product synthesis, from Robinson s 1917 tropinone synthesis to Eschenmoser and Woodward s 1973 coenzyme synthesis, metal-catalyzed reactions played no great role. In contrast, modern organic syntheses often involve numerous transition metal-catalyzed steps. Main-group compounds, such as BuLi, MeMgBr, or NaBH4, tend to act in stoichiometric quantity as reagents, while the more expensive transition metals, typically complexes of Pd, Rh, or Ru, tend to be used as catalysts and therefore in much lower amounts, for example, 0.1-5 mol% (mmol catalyst per 100 mmol substrate). 

Catalytic asymmetric methylation of 6,7-dichloro-5-methoxy-2-phenyl-l-indanone with methyl chloride in 50% sodium hydroxide/toluene using M-(p-trifluoro-methylbenzyDcinchoninium bromide as chiral phase transfer catalyst produces (S)-(+)-6,7-dichloro-5-methoxy-2-methyl-2--phenyl-l-indanone in 94% ee and 95% yield. Under similar conditions, via an asymmetric modification of the Robinson annulation enqploying 1,3-dichloro-2-butene (Wichterle reagent) as a methyl vinyl ketone surrogate, 6,7 dichloro-5-methoxy 2-propyl-l-indanone is alkylated to (S)-(+)-6,7-dichloro-2-(3-chloro-2-butenyl)-2,3 dihydroxy-5-methoxy-2-propyl-l-inden-l-one in 92% ee and 99% yield. Kinetic and mechanistic studies provide evidence for an intermediate dimeric catalyst species and subsequent formation of a tight ion pair between catalyst and substrate. 

Peter Hervey Given was bom in 1918. He was educated at Oxford University, receiving a B.A. in Chemistry in St. Peter s Hall, Oxford, and the M.A. and D.Phil. in the Dyson Perris Laboratory under the direction of Professors D. LI. Hammick and Sir Robert Robinson (who was the Nobel laureate in chemistry for 1947). Given s thesis research dealt with carbonium ion reactions of aromatic hydrocarbons on cracking catalysts (1-. ... 

This asymmetric phase-transfer method has been applied to enantio-selective Robinson annelation as shown in Scheme 14 (41). First, alkylation of a 1-indanone derivative with the Wichtetie reagent as a methyl vinyl ketone equivalent in the presence of p-CF3BCNB gives the S-alkylation product in 92% ee and 99% yield. With 1 -(p-trifluoro-methylbenzyl)cinchonidinium bromide, a pseudo-enantiomeric diaste-reomer of p-CF3BCNB, as catalyst, the -alkylation product is obtained in 78% ee and 99% yield. These products are readily convertible to the... 

The indium trichloride-catalyzed Mukaiyama aldol reaction of 3-aminoketoesters with various silylenolethers gave under solvent-free conditions 1,3-amino alcohols with high stereoselectivity [36], Several Robinson annelation reactions have been carried out enantio-selectively using (S)-proline as a chiral catalyst [37]. Remarkably, the enantioselectivity was distinctly higher in the absence of solvent than in DMSO. 

Using (2) as catalyst provided the (R) enantiomer in 99% yield, 78% ee. The key introduction of asynunetry during the synthesis of (+)-podocarp-8(14)-en-13-one was the phase-transfer-catalyzed Robinson annulation of 6-methoxy-l-methyl-2-tetralone with ethyl vinyl ketone. The authors carried out a comparative study of the A/-(4-trifluoromethyl)benzyl derivatives of cinchonine, cinchonidine, dihydrocinchonine, and dihydrocinchonidine and found that (5) produced the highest ee of the desired (S) enantiomer at —45 °C using toluene and 60% aq KOH (eq 10). ... 

This particular product of the Robinson annelation is an important intermediate for the synthesis of natural products. The natural products exist as a single enantiomer so to be useful this material must also be a single enantiomer. A remarkably efficient preparation employs (S)-proline as the catalyst for the asymmetric... 

The structure of (21) is reminiscent of Robinson annelation product (14), a readily available starting material (Chapter 21), Reduction of one ketone (see page 318) gives (15), converted at once to a tosylate (22) for later elimination. Hydrogenation requires the double bond of (22) to lie flat on the catalyst surface (Chapter 12) and this is possible only from the outside of the bowl (see 22a) giving c s-decalone (23). 

Lewis, L.S., A.B. Norman, and A. Robinson The evaluation of palladium/copper catalysts for CO removal ... 

It was at Winnington, the home of the Alkali Group of ICI, that polythene, Id s major discovery before the Second World War, was taken from laboratory experiments to large-scale production. Several Oxonians played an important role. Firstly, in 1931 Robinson, who was a consultant to Id s Dyestuffs group, suggested that several reactions be tried under very high pressures without catalysts. One reaction in his list was that between ethylene and benzaldehyde. The work he outlined was done at Winnington by... 

A more efficient approach to control the stereochemical outcome for the Robinson annulation can be through the use of chiral catalysts such as in the case of the enantioselective Hajos-Wiechert variation introduced earlier. There are other chiral agents other than the popular (S)-proline-mediated annulation reaction that are used for these transformations—for example the use of (Bronsted acid such as trifluoroacetic (TFA). This new catalyst for the Robinson annulation was reported in 2007 by Endo et. al., where the Bronsted acid, contrary to Hajos-Wiechert reaction, gives the (i )-isomer of the Wieland-Miescher ketone 44 in a moderate yield of 47% and 75% ee. 

In 2009 Miro et al. reported the use of phosphoric acids as a chiral catalyst for enantioselective transformation of the Robinson annulation. Chrial phosphoric acids 61 and 62 are used in sequence first for the Michael reaction step and are then followed by the cyclization step. Synthesis of the aimulation adduct 64 is shown as an example in the group s report. The cyclized adduct is formed from the reaction of the P-keto ester 63 in the presence of the phosphoric acid 61 at 40 °C for 24 h and is followed by... 

Michael reaction with an o , S-unsaturated ketone followed by an intramolecular aldol reaction has proven to be a valuable method for the synthesis of 2-cyclohexenones. An especially important example of a Michael-aldol sequence is the Robinson annulation, in which treatment of a cyclic ketone, 8-ketoester, or S-diketone with an a,)8-unsaturated ketone in the presence of a base catalyst forms a cyclohexenone ring fused to the original ring. When the following racemic 8-ketoester, for example, is treated with methyl vinyl ketone in the presence of sodium ethoxide in ethanol, the Michael adduct forms and then, in the presence of sodium ethoxide, undergoes a base-catalyzed intramolecular aldol reaction followed by dehydration to give a racemic substituted cyclohexenone. 

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