5-Bromo-l-pentene

In a typical example of the malonic ester synthesis, 6-heptenoic acid has been prepared from 5-bromo-l-pentene ... 

H2C=CHCH2CH2CH2Bt -I- CH2(COOCH2CH3)2 5-Bromo-l-pentene Diethyl malonate... 

It has been shown that halogen-substituted alkenes can participate in the metathesis reaction, e.g. 5-bromo-l-pentene reacts with 2-pentene 11). A very interesting reaction is the conversion of methyl-9-octa-decenoate into 9-octadecene and dimethyl-9-octadecenedioate 12) ... 

Addition of halocarbons to alkenes in the presence of transition metals is a well-known radical reaction. Weinreb etal. have now reported an intramolecular version leading to cyclic esters or bicyclic lactones. Typical substrates are the a,a-dichloro ester 1 or the a,a-dichloro acid 2, readily available by reaction of ethyl lithiodi-chloroacetate with 5-bromo-l-pentene. When 1 is heated in benzene at 160° with a metal catalyst, mixtures of epimeric ot,w-dichloro esters 3 and 4 are obtained. The ratio and yields of 3 and 4 are dependent on the catalyst and concentration of 1, but 3 and 4 are the major products formed in the presence of Ru(II) and Fe(II) catalysts. In contrast cyclization of 2 under the same conditions gives the bicyclic y-lactone 5 in high yield. 

H2C=CHCH2CH2CH2Br + CH2(COOCH2CH3)2 Na H,> H2C=CHCH2CH2CH2CH(COOCH2CH3)2 5-Bromo-l-pentene Diethyl malonate Diethyl 2-(4-pentenyl)malonate (85%)... 

Methoxyethylidene)-/3-o- Ether Toluene TBABA 90 5-Bromo-l-pentene — 71 0 122... 

Vinyltrimethylsilane (97%), trimethylchlorosilane (98%), chlorodimethylsilane (97%), bromoform (96%), 5-bromo-l-pentene (95%), nBuLi (2.5M solution in hexanes), MeLi (1.6M solution in diethyl ether), n-decane (puriss. p.a., standard for GC, > 99.8%) and hexachloroplatinic(lV) acid hydrate were purchased from Aldrich. Platinum divinyltetramethyldisiloxane complex (Karstedt s catalyst, 3% solution in xylenes), hexamethyl-cyclotrisiloxane (95%), vinylmethyldichlorosilane (97%) and 1,1,3,3-tetramethyldisiloxane (97%) were bought from ABCR. Bromine (puriss) was bought from Eluka. Triethylamine (pure for analysis) and zinc oxide (pure) was purchased from Chempur. Solvents (tetrahydrofurane, diethyl ether, methylene chloride, pentane, ethyl acetate) were supplied by POCh (Polish Chemical Reagents). 

An isolated halogen atom is unaffected by zinc under the conditions of the reaction. Thus, 1,2,5-tribromopentane gives the halo olejin, 5-bromo-l-pentene (71%). ... 

The last example consists of the synthesis of lycorane skeletons by an intramolecular cycloaddition of the azomethine ylide generated by the decarboxylation route (Section II,E). Thus, 3,4-(methylenedioxy)phenyIaceto-nitrile is deprotonated with LDA and then alkylated with 5-bromo-l-pentene... 

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. 

Apart from halogen substituted alkenes, heteroatoms normally deactivate catalytic systems. However the synthetic utility of such reactions has encouraged further research in this field. Chlorine substitution at vinylic positions deactivates the double bond but halogen substituted alkenes in which the double bond is in an position undergo cross metathesis with internal alkenes. For example, 5-bromo-l-pentene undergoes cross metathesis with 2-pentene. Unsaturated compounds containing ester groups also react, e.g. methyl-9-octadecenoate is converted to 9-octadiene and dimethyl-9-octadecenedioate by the WCl —Sn(CH3)4 catalytic combination [15]. 

Cyclic ethers can be prepared by the intramolecular Sj j2 reaction of a halogen-substituted alcohol such as a bromo alcohol. Proton transfer to a base such as sodium hydroxide gives a bromo alkoxide. If the solution is dilute, the alkoxide acts as a nucleophile, and an intramolecular reaction displaces a bromide ion. This process is shown below for 5-bromo-l-penten-l-ol. 

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