Cyclopentenes rhodium

The diester 226 undergoes ring-closure to the methylenecyclopentane derivative 227 in the presence of a catalytic amount of chlorotris(triphenylphosphine)rhodium in boiling chloroform saturated with hydrogen chloride. In contrast, if the reaction is catalysed by palladium(II) acetate, the isomeric cyclopentene 228 is produced (equation 115)118. 

The 0/7/fo-alkylation of aromatic ketones with olefins can also be achieved by using the rhodium bis-olefin complex [C5Me5Rh(C2H3SiMe3)2] 2, as shown in Equation (9).7 This reaction is applied to a series of olefins (allyltrimethyl-silane, 1-pentene, norbornene, 2,2 -dimethyl-3-butene, cyclopentene, and vinyl ethyl ether) and aromatic ketones (benzophenone, 4,4 -dimethoxybenzophenone, 3,3 -bis(trifluoromethyl)benzophenone, dibenzosuberone, acetophenone, />-chloroacetophenone, and />-(trifluoromethyl)acetophenone). 

It took another decade however before the idea of developing a rhodium-catalyzed olefin hydroboration process came to fruition. This occurred in 1985 when Mannig and Noth reported the first examples of such a process.8 They discovered that Wilkinson s catalyst 2 was effective for the addition of catecholborane 1 to a range of alkenes and alkynes, as exemplified by cyclopentene 4 (Scheme 2). 

Ojima has reported a rhodium-catalyzed protocol for the disilylative cyclization of diynes with hydrosilanes to form alkylidene cyclopentanes and/or cyclopentenes. As an example, reaction of dipropargylhexylamine with triethyl-silane catalyzed by Rh(acac)(GO)2 under an atmosphere of CO at 65 °G for 10 h gave an 83 17 mixture of the disilylated alkylidene pyrrolidine derivative 92b (X = N-//-hexyl) and the disilylated dihydro-1/ -pyrrole 92c (X = N-//-hexyl) in 76% combined yield (Equation (60)). Compounds 92b and 92c were presumably formed via hydrosilyla-tion and hydrosilylation/isomerization, respectively, of the initially formed silylated dialkylidene cyclopentane 92a (Equation (60)). The 92b 92c ratio was substrate dependent. Rhodium-catalyzed disilylative cyclization of dipro-pargyl ether formed the disilylated alkylidene tetrahydrofuran 92b (X = O) as the exclusive product in low yield, whereas the reaction of dimethyl dipropargylmalonate formed cyclopentene 92c [X = C(C02Et)2] as the exclusive product in 74% isolated yield (Equation (60)). 

Ethyl diazoacetate, 117 Rhodium(II) carboxylates, 266 Cyclopentenes by reaction of Wittig reagents with dicarbonyl compounds... 

Lower temperatures are enough with a strong Lewis acid like Et2AlCl. The cyclopropane 52 comes from available dihydrofuran 50 by rhodium-catalysed carbene insertion. Rearrangement at very low temperatures gives the cyclopentene 53 that actually has three five-membered rings fused together.13... 

Materials. (Bicyclo[2.2.1]hepta-2,5-diene) rhodium(I) chloride dimer and silver hexafluorophosphate were purchased from Strem Chemical the rhodium complex was recrystallized from acetone prior to use. All silanes (Aldrich) were distilled under a nitrogen atmosphere, freeze-thaw degassed and stored under a nitrogen atmosphere. 4-cyclopentene-l,3-dione (CPDK) from Aldrich was recrystallized from diethyl ether and stored in the dark under a nitrogen atmosphere at -40°C. All solvents were distilled under nitrogen from appropriate drying agents immediately prior to use. 

Metal-promoted vinylcyclopropane C3 - C5 ring expansions have been reported. Thus, ethyl 2-methoxy-2-vinylcyclopropanecarboxylate 393 rearranged to a 2 1 mixture of 3-methoxy-2-cyclopentenecarboxylate 396 and 3-methoxy-3-cyclopentene-carboxylate 397 on heating at 160 °C in the presence of catalytic amounts of copper bronze or copper(I) chloride in contrast, platinum and rhodium complexes catalyzed... 

Unhindered simple olefins are usually rapidly hydrogenated under very mild conditions over platinum metal catalysts such as platinum, palladium, and rhodium as well as over active nickel catalysts such as Raney Ni, nickel boride, and Urushibara Ni. For example, 0.1 mol of cyclohexene is hydrogenated in 7 min over 0.05 g of Adams platinum oxide in ethanol at 25°C and 0.2-0.3 MPa H2 (eq. 3.1).5 1-Octene and cyclopentene (eq. 3.2) are hydrogenated in rates of 11.5 and 8.6 mmol (258 and 193 ml H2 at STP) g Ni 1-min 1, respectively, over P-1 Ni in ethanol at 25°C and 1 atm H2.18 Hydrogenation of cyclohexene over active Raney Ni proceeds at rates of 96-100 ml H2 at STP (4.3-4.5 mmol) g Ni min-1 in methanol at 25°C and 1 atm H2 49,50 and can be completed within a short time, although usually larger catalyst substrate ratios than required for platinum catalyzed hydrogenations are employed (eq. 3.3).50... 

This collection begins with a series of three procedures illustrating important new methods for preparation of enantiomerically pure substances via asymmetric catalysis. The preparation of 3-[(1S)-1,2-DIHYDROXYETHYL]-1,5-DIHYDRO-3H-2.4-BENZODIOXEPINE describes, in detail, the use of dihydroquinidine 9-0-(9 -phenanthryl) ether as a chiral ligand in the asymmetric dihydroxylation reaction which is broadly applicable for the preparation of chiral dlols from monosubstituted olefins. The product, an acetal of (S)-glyceralcfehyde, is itself a potentially valuable synthetic intermediate. The assembly of a chiral rhodium catalyst from methyl 2-pyrrolidone 5(R)-carboxylate and its use in the intramolecular asymmetric cyclopropanation of an allyl diazoacetate is illustrated in the preparation of (1R.5S)-()-6,6-DIMETHYL-3-OXABICYCLO[3.1. OJHEXAN-2-ONE. Another important general method for asymmetric synthesis involves the desymmetrization of bifunctional meso compounds as is described for the enantioselective enzymatic hydrolysis of cis-3,5-diacetoxycyclopentene to (1R,4S)-(+)-4-HYDROXY-2-CYCLOPENTENYL ACETATE. This intermediate is especially valuable as a precursor of both antipodes (4R) (+)- and (4S)-(-)-tert-BUTYLDIMETHYLSILOXY-2-CYCLOPENTEN-1-ONE, important intermediates in the synthesis of enantiomerically pure prostanoid derivatives and other classes of natural substances, whose preparation is detailed in accompanying procedures. 

On heating at 160°C in the presence of catalytic amounts of copper bronze or copper(l) chloride, ethyl 2-methoxy-2-vinylcyclopropanecarboxylates (220) undergo ring expansion into the isomeric 3-methoxy-2-cyclopentene (221) and 3-methoxy-3-cyclo-pentenecarboxylates (222) equation 146) on the other hand platinum and rhodium complexes catalyse the ring-opening into ethyl-4-methoxy-3,5-hexadienoate. ... 

The addition of trimethylphosphine to these rhodium/zeolite catalysts destroyed all catalytic activity because the phosphine was small enough to fit into the zeolite cavity and could deactivate all of the rhodium in the catalyst. The bulky tributylphosphine, however, could not enter the cavity and, thereby, only blocked the external rhodium from further reaction. This specific blocking enhanced the selectivity in the hydrogenation of a mixture of cyclopentene and 4-methylcyclohexene over a Rh/ZSM-11 catalyst. After treatment of the catalyst with tributylphosphine to block the external catalytically active sites, only the... 

Rhodium-catalyzed cyclopentene formation has been observed in cyclopropanations of enol ethers 8 and found to depend on the nature of the ligand and the ester of the diazo compound 9 42,43 Cyclopentenes 10 were isolated exclusively with 2,6-di-ter -butyl-4-methylphenyl esters. 

Lewis acid catalysis of the vinylcyclopropane rearrangement has been reported for vinylcy-clopropane 3, a key intermediate in the synthesis of the plant hormone antheridogen-An. Most recently, a report has appeared describing a highly stereoselective, diethylaluminum chloride promoted rearrangement of vinylcyclopropanes 5 to cyclopentenes 6. The cyclopen tenes appear to be formed directly, in some cases as a consequence of the rhodium-promoted cyclopropanation of enol ethers (see Section 2.4.3.1.3.). ... 

Cyclopropyl ketones are readily isomerized to dihydrofuran derivatives thermally or under catalytic conditions.For example, cyclopropyl ketones 2 and 4 yield dihydrofurans 3 and 5, respectively, thermally or under rhodium catalysis. Such rearrangements occur normally under acid catalysis whereas thermolysis favors the vinylcyclopropane to cyclopentene rearrangement, except for highly functionalized (R = SOjPh) cyclopropanes. 

Hydroformylation of the water-insoluble oleyl alcohol into formylstearyl alcohol has also been successfully achieved with a 96.6% yield by using a rhodium/trisul-fonated triphenylphosphine complex dissolved in an aqueous film supported on a high-surface-area silica gel (cf. Section 6.1) [13]. This supported catalyst has also been used to perform the hydroformylation of allyl 9-decenyl ether and 3-methyl-2-(2-pentenyl)-2-cyclopenten-l-one (as-jasmone). However, with the latter substrate, the aldehyde yields did not exceed 38% [14],... 

A small number of enantiomerically pure Lewis acid catalysts have been investigated in an effort to develop a catalytic asymmetric process. Initial work in this area was carried out by Narasaka and coworkers using the titanium complex derived from diol (8.216) in the cycloaddition of electron-deficient oxazolidinones such as (8.217) with ketene dithioacetal (8.218), alkenyl sulfides and alkynyl sulfides. Cyclic alkenes can be used in this reaction and up to 73% ee has been obtained in the [2- -2] cycloaddition ofthioacetylene (8.220) and derivatives with2-methoxycarbonyl-2-cyclopenten-l-one (8.221) usingthe copper catalyst generated with bis-pyridine (8.222). Furthermore, up to 99% ee has been obtained in the [2-1-2] cycloaddition of norbornene with alkynyl esters using rhodium/Hs-BINAP catalysts. This reaction is not restricted to the use of transition metal-based Lewis... 

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