Cyclohexene solid support

In a detailed investigation, Turner and coworkers have described the preparation and application of solid-supported cyclohexane-1,3-dione as a so-called capture and release reagent for amide synthesis, as well as its use as a novel scavenger resin [125]. Their report included a three-step synthesis of polymer-bound cyclohexane-1,3-dione (CHD resin, Scheme 7.104) from inexpensive and readily available starting materials. The key step in this reaction was microwave-assisted complete hydrolysis of 3-methoxy-cyclohexen-l-one resin to the desired CHD resin. 

They found that the erythrolthreo-% i,cX N Xtj is X-substituent dependent, acting through H-bonding, which was demonstrated by the TFDO Ic epoxidation of 73. An example of cyclohexene epoxidation by dioxiranes derived from various ketones grafted on solid supports has also appeared <1996MI273>. Shi and co-workers reported <1996JA9806> excellent ee s of asymmetric epoxidation of different /ra t-olefms by fructose-derived ketones 74 before then, only low enantioselectivities (9-20%) have been reported on this type of reaction. 

Fig. 4.1. Chromatograms of the original sample (I) and the products of hydrogenation at 200°C (II) and dehydrogenation at 325°C (III) [55]. Carrier gas, hydrogen flow-rate, 60 ml/min column, 600 X 0.6 cm I.D. sorbent, 20% polyethylene glycol 4000 on solid support. Peaks 1 = air 2 =n-octane 3=octene-l 4 = octene-2 5 = n-propylcycIopentene-1 6 = cyclohexene 7 = 1-isopropylcyclo-hexene-l 8 =n-propylcyclohexene 9 = ethylcyclohexene 10 = isopropylcyclohexane 11 = product from the dehydrogenation of propylcyclopentane 12 = n-octane 13 = ethylbenzene 14 = isopropylbenzene. From ref. 55,...

For the Ti(OiPr)4/silica system, the advantage of MCM-41 (a mesoporous silica) over an amorphous silica is not evident either in terms of activity or selectivity for the epoxidation of cyclohexene with H202 in tert-butyl-alcohol.148 Nevertheless, deactivation of the catalysts seems slower, although the selectivity of the recovered catalysts is also lower (allylic oxidation epoxidation = 1 1). Treatment of these solids with tartaric acid improves the properties of the Ti/silica system, but not of the Ti/MCM-41 system, although NMR,149 EXAFS,150 and IR151 data suggest that the same titanium species are present on both supports. 

In another example, a polymer-supported chromium porphyrin complex was supported on ArgoGel Cl and then employed for the ring-opening polymerization of 1,2-cyclohexene oxide and C02 [95], This complex showed higher activity than a C02-soluble equivalent, and the solid nature of the catalyst meant that recycling of the catalyst was much easier. 

A continuous procedure for the alkylation of mesitylene and anisole with supercritical propene, or propan-2-ol in supercritical carbon dioxide, with a heterogeneous polysiloxane-supported solid acid Deloxan catalyst has been reported giving 100% selectivity for monoalkylation of mesitylene with 50% conversion at 250 °C and 150 bar by propan-2-ol in supercritical carbon dioxide. p-Toluenesulfonic acid monohydrate has been demonstrated as an efficient catalyst for the clean alkylation of aromatics using activated alkyl halides, alkenes or tosylates under mild conditions. Cyclohexene, for example, reacts with toluene to give 100% cyclohexyltoluenes (o m p-29 18 53) under these circumstances. 

The same authors (77) also investigated the Michael addition of nitromethane to a,/l-unsaturated carbonyl compounds such as methyl crotonate, 3-buten-2-one, 2-cyclohexen-l-one, and crotonaldehyde in the presence of various solid base catalysts (alumina-supported potassium fluoride and hydroxide, alkaline earth metal oxides, and lanthanum oxide). The reactions were carried out at 273 or 323 K the results show that SrO, BaO, and La203 exhibited practically no activity for any Michael additions, whereas MgO and CaO exhibited no activity for the reaction of methyl crotonate and 3-buten-2-one, but low activities for 2-cyclohexen-l-one and crotonaldehyde. The most active catalysts were KF/alumina and KOH/alumina for all of the Michael additions tested. 

Diels-Alder reactions have been conducted on solid phase, with either the dieno-phile or the diene linked to the support [156]. The reaction conditions and the regio-and stereoselectivities observed are similar to those in solution [58,157,158]. Illustrative examples of Diels-Alder reactions leading to support-bound cyclohexenes are listed in Table 5.10. Further examples include the cycloaddition of polystyrene-bound 2-sulfonyl-l,3-butadiene and V-phenylmaIcimidc [51], the high-pressure cycloaddition of 1,3-butadienes to resin-bound 1 -nitroacrylates [95], and the intramolecular Diels-Alder reaction of styrenes with acrylates [159]. 

Anchoring Mn(TPP)OAc to a rigid polyisocyanide support has resulted in a considerable increase in the epoxidation rate of cyclohexene by NaOCl. These solid catalysts can be recovered and retain their activity during several consecutive experiments.522... 

For these two reactions, the activity of 2 is of the same order of magnitude as that of supported Ti based catalysts this is rather unusual and was never reported so far [13].The selectivity for cyclohexene epoxide is high ([epoxide]/[diol] 8) as is the selectivity for dihydroxybenzenes, when these results are compared with those obtained with Ti based amorphous solids. Finally, for both reactions, no Zr was detected in the catalytic solutions and the solids could be recycled after simple filtration, without significant loss of activity and selectivity. 

In recent years the Asahi Corporation has developed a benzene-to-cyclohexene process involving a liquid-liquid two-phase system (benzene-water) with a solid ruthenium catalyst dispersed in the aqueous phase. The low solubility of cyclohexene in water promotes rapid transfer towards the organic phase. An 80000 t annum plant using this process is in operation. Another way to scavenge the intermediate cyclohexene is to support the metal hydrogenation catalyst on an acidic carrier (e. g. silica-alumina). On such a bifunctional catalyst the cyclohexene enters catalytic alkylation of the benzene (present in excess) to yield cyclohexylbenzene [19], which can be converted, by oxidation and rearrangement reactions, into phenol and cyclohexanone. 

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