4-Pentenyl ethers

Bridged calix[4]arenes in which two phenolic hydroxyl groups are derivatized as 4-pentenyl ethers undergo RCM in the presence of a carbene complex 2." Another impressive result concerns the construction of a cylindrical tricyclic peptide. This compound contains a 38-membered ring and is formed in 65% yield on exposure to 1. The two-step reaction involves RCM in the final stage. 

In the area of cyclodextrin ethers the -compound has been converted into a set of five tris-Tbdms ethers, all substituted at their various 6-positions, which were separated by hplc and characterized by n.m.r. spectroscopy. Related work applied to y-cyclodextrin gave the various 6,6 -disubstituted ethers. 5-Bromo-l-pentene was used to produce the 2-0-mono-4-pentenyl ether of P-cyclodextrin which was then permethylated and the product was chemically bonded to silica gel to form an efficient hplc stationary phrase for the separation of enantiomers. Peroctyl a-cyclodextrin has been studied as a chiral receptor for the ephedrinium ion. Various octyl ethers of a-, P- and y-cyclodextrin ranging in their substitution from the diethers to completely alkylated products were characterized by electrospray mass spectrometry and n.m.r. methods applied to methylated derivatives. The 2,6-didodecyl derivative of p-cyclodextrin has been used as a potentiometric sensor. In the field of aromatic ethers, naphthyl carboxylate substituents have been bonded at the 6-positions and the products were able to transfer excitation energy to complexed merocyanine held in the cavities of those molecules. These phototransfer processes were extremely efficient.P-Substituted cyclodextrin derivatives with p-allyloxybenzoyl or various benzyl substituents at 0-2 or 0-3 were incorporated by hydrosilylation to give hydromethylpolysiloxane polymers used as chiral phases for chromatographic resolution of enantiomers. Cyclodextrins with complex benzyl-like eth are illustrated in 22 and 23. The latter were prepared as artificial redox enzymes. 

Thus, in the presence of 2 mol % Ni dibromide or dichloride complexes of (- -)-(J ,l )-cyclopentane-l,2-diylbis(diphenylphosphine) (26),reaction of cyclo-pentenyl ether 28 with EtMgBr results in the formation of 1-ethylcyclopentene (S)-29 in 91% yield and with 83% ee. Higher levels of enantiocontrol are observed when (l )-6,6 -dimethylbiphenyl-2,2 -diyl)bisdiphenylphosphine (bi-... 

In contrast, using a rhodium complex as the catalyst, a [4+2] cycloaddition occurs with formation of the pentenyl ethers 272 in 92-93 % yields as a result of a reductive elimination. 

NBS, CH3CN, H2O, 62-90% yield.The POM group has been selectively removed in the presence of an ethoxy ethyl ether, TBDMS ether, benzyl ether, p-methoxybenzyl ether, an acetate, and an allyl ether. Because the hydrolysis of a pentenyl 2-acetoxyglycoside was so much slower than a pentenyl 2-benzyloxyglycoside, the 2-benzyl derivative could be cleaved selectively in the presence of the 2-acetoxy derivative. The POM group is stable to 75% AcOH, but is cleaved by 5% HCl. 

A solution of 3.7I g (0.013 mol) of tributyltin hydride in 10 mL benzene is added dropwise to a solution of 3.09 g (0.011 mol) of S-[(S)-4-(benzyloxy)-3-pentenyl] 5-methyl carbonodithioate in 25 mL of degassed, anhyd benzene under an atmosphere of argon, followed by 5 mg of AIBN. The mixture is heated under reflux for 2.5 h and then is concentrated under reduced pressure. Flash chromatography of the residue using ht,0/petroIeum ether 1 50 containing 1 % triethylamine as eluant gives a colorless oil yield 3.87 g (78%) [a] - 26 (e = 1. CHCl3). 

When the chain bearing the allylsilane is one carbon longer, i.e., by the use of pentenylsilanes, cycloheptane rings can be formed. Both the (Z)- and (A )-isoiner of the (3-pentenyl)silanes can be synthesized selectively, but only the (Z)-(3-pentenyl)silane cyclized stereospecifically (complete 1,4-asymmetric induction). Both cthylaluminum dichloride and boron trifluoride diethyl ether complex promote the seven-membered ring formation35 43-48. 

To a solution of 310 mg (1.18 mmol) of 4-[(Z)-5-(trimethylsilyl)-3-pentenyl]-3-vinyl-2-cyclohcxcnone in 20 mL of toluene is added at —78, JC 0.75 mL (2.75 mmol) of a 50% solution of ethylaluminum dichloride in hexane. After stirring for 2 h at — 78 C. the mixture is quenched by addition of 20 mL of sat. aq NaHC Oj. After washing with 20 mL of brine the organic phase is extracted with three 30-mL portions of diethyl ether and dried over MgS04. The solvent is removed and the crude product is flash chromatographed (silica gel, EiOAc/petroleum ether 1 9) yield 114 mg (60%). 

Pentenyl amides such as 15A cyclize to lactams 15B on reaction with phenyl selenenyl bromide. The 3-butenyl compound 15C, on the other hand, cyclizes to an imino ether 15D. What is the basis for the differing reactions ... 

C. 4-Ketop/pecolic acid hydrochloride. tert-Butyl [1-(tert-butoxycarbonyl)-3-oxo-4-pentenyl]carbamate, 8.73 g (0.0308 mol), is dissolved in 280 mL of an ice-cooled, saturated solution of hydrogen chloride in ether. The solution is kept without stirring at room temperature overnight. The resulting suspension is filtered and the... 

The formation of 3-methyltetrahydropyran-2-ol from the pentenyl methyl ether (234) proceeds in an analogous manner since hydrolysis of the enol ether to the pentanal occurs prior to cyclization (79JOC364). 

Either way, ether analog 25 was expected to be more reactive, and indeed, 28 was found to cyclize quite efficiently with a rate constant for cyclization of 3.8 ( 0.3) X 105 s 1 [140]. Only the exo-mode of cyclization was observed, in contrast to Piccardi s results. Further studies of fluorinated 4-pentenyl and cyclobutylcarbinyl radical systems will hopefully provide eventual definitive insight into those factors which govern rates and equilibria in this system. 

Purify the crude product by chromatography using pentane ether (4 1). Pure frans-1-(hydroxymethyl)-2-methyl-2-(4-methyl-3-pentenyl)cyclopropane is obtained as a colourless oil (940 mg, 80%). Characterize the product by 1H and 13C NMR. 

Boron trifluoride etherate (0.37 ml, 3 mmol) was added to a benzene (33 ml) solution of 4-pentenyl iodoacetate (1.0 mmol) under a nitrogen atmosphere at room temperature. Z Lv(tributyltin) (0.1 mmol) was added and the mixture was irradiated with a 300 W sun lamp at 20 °C. After 6 h, the solvent was removed and the residue was chromatographed on silica gel (hexane /ethyl acetate = 2/1) to produce the iodolactone in 80% yield [234]. 

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