3-Hydroxy-1-alkene

A closely related reaction has been performed with other aldehydes and even with ketones without a catalyst, but with heat. The aldehydes and ketones here are active ones, such as chloral and acetoacetic ester. The product in these cases is a 3-hydroxy alkene, and the mechanism is pericyclic ... 

This reaction is reversible and suitable p-hydroxy alkenes can be cleaved by heat (17-34). There is evidence that the cleavage reaction occurs by a cyclic mechanism (p. 1351), and, by the principle of microscopic reversibility, the addition mechanism should be cyclic too. Note that this reaction is an oxygen analog of the ene... 

When pyrolyzed, P-hydroxy alkenes cleave to give alkenes and aldehydes or ketones. Alkenes produced this way are quite pure, since there are no side reactions. The mechanism has been shown to be pericyclic, primarily by observations... 

Esterbauer, H., Zollner, H. and Schaur, R.J. (1988). Hydroxy-alkenals cytotoxic products of lipid peroxidation. Atlas of Science Biochemistry 1, 311-319. 

Perlmutter used an oxymercuration/demercuration of a y-hydroxy alkene as the key transformation in an enantioselective synthesis of the C(8 ) epimeric smaller fragment of lb (and many more pamamycin homologs cf. Fig. 1) [36]. Preparation of substrate 164 for the crucial cyclization event commenced with silylation and reduction of hydroxy ester 158 (85-89% ee) [37] to give aldehyde 159, which was converted to alkenal 162 by (Z)-selective olefination with ylide 160 (dr=89 l 1) and another diisobutylaluminum hydride reduction (Scheme 22). An Oppolzer aldol reaction with boron enolate 163 then provided 164 as the major product. Upon successive treatment of 164 with mercury(II) acetate and sodium chloride, organomercurial compound 165 and a second minor diastereomer (dr=6 l) were formed, which could be easily separated. Reductive demercuration, hydrolytic cleavage of the chiral auxiliary, methyl ester formation, and desilylation eventually led to 166, the C(8 ) epimer of the... 

Bol and Liskampl"2 introduced the [2,3]-Wittig rearangement in order to install the re-giochemistry of the alkene and the oxygenation of the incipient C-terminus in one operation. A racemic P-Al-trityl-a-hydroxy-( )-alkene 117 (R = H R2=Me) was prepared from cro-... 

Catalytic oxy-palladation is an extremely useful method for the synthesis of functionalized THF and tetrahydropyran moieties. This reaction is brought about simply by treating a 1,4- or 1,5-hydroxy alkene with 0.1 mol-eq of Pd(II) salts and copper(I) chloride in DMF, with oxygen (equation 181)655. If this reaction is carried out in the presence of carbon monoxide in methanol, then an ester moiety is introduced into the product molecule (equation 182)656-658. If an alkene is introduced in place of the CO, then a tandem vinylation reaction also takes place (equation 183)659. 

A simple example involves the reaction of the silyl ether 213, made from the corresponding 4-hydroxy-alkene by treatment with (bromomethyl)chloro-dimethylsilane, with tributyltin hydride and a radical initiator. Bromine abstraction and intramolecular cyclization with the double bond leads to the bicyclic 214, which upon oxidation with hydrogen peroxide gives the branched-chain 215 in an overall yield of 73% from the alcohol precursor of 213 (Scheme 21). When the sequence is conducted with the C-4 epimeric starting alcohol, the final product again has the hydroxymethyl group cis-related to the hydroxy group.217... 

Hydroxy alkenals affect adenylate cyclase activity and phospholipase C activities reduce cell growth and promote cell differentiation inhibit platelet aggregation block macrophage action block thiol group... 

Backvall and co-workers have demonstrated that m-annulated furans are obtained in excellent yields from 7-hydroxy alkenes by Pd(ll)-catalyzed oxidative heteroatom cyclization (Equation 83) <1995TL7749>. The scope of the Pd(ll) catalyst system with O2 in DMSO as reoxidant has been demonstrated with ring sizes five to seven (n = 1-3). 

The products obtained from the oxymercuration-demercuration of alkenylacetates under standard conditions (NaBH4/NaOH 3 M) are diols. However, the yields are significantly lower than with methoxy-and hydroxy-alkenes because of competitive deoxymercuration.Increasing the amount of base results in major increases in the yield of hydrated products. A less basic procedure has been developed, which allows for the survival of the acetate group. 

A typical analysis of L. fendleri seed oil showed the presence of 16 0 (1%), 18 0 (2%), 18 1 (15%), 18 2 (7%), 18 3 (14%), lesquerolic (54%), and auricolic (4%) acids. As lesquerolic acid is the C20 homologue of ricinoleic with the same p-hydroxy alkene unit, it undergoes similar chemical reactions but produces (some) different products. For example, pyrolysis should give heptanal and 13-tri-decenoic acid (in place of 11-undecenoic acid). This could be converted to 13-ami-notridecanoic acid, the monomer required to make nylon-13. Similarly, alkali-fusion will give 2-octanol and dodecanedioic acid in place of decanedioic (sebacic) acid. This C12 dibasic acid is aheady available from petrochemical products and has a number of applications. A recent account of the status of this oil is available (126). 

Pyrolysis of p-Hydroxy Alkenes O-Hydro-C-allyl-elimination... 

When pyrolyzed, p-hydroxy alkenes cleave to give alkenes and aldehydes or ketones." Alkenes produced this way are quite pure, since there are no side reactions. The mechanism has been shown to be pericyclic, primarily by observations that the kinetics are first order" and that, for ROD, the deuterium appeared in the allylic position of the new alkene." This mechanism is the reverse of that for the oxygen analog of the ene synthesis (16-54). p-Hydroxyacetylenes react similarly to give the corresponding allenes and carbonyl compounds." " The mechanism is the same despite the linear geometry of the triple bonds. 

FIGURE 21.4 Schematic diagram of reactive hydroxy-alkenals generated during lipid peroxidation of n 3 and n-6 polyunsaturated fatty... 

The first Pd-catalyzed carboamination and carboetherification reactions of y-amino or y-hydroxy alkenes with aryl halides were described by Wolfe in 2004 [ 100]. As shown below, treatment of these substrates with aryl or heteroaryl bromides in the presence of NaOfBu and a palladium catalyst provides substituted tetrahydrofuran or pyrrolidine products. 

Hydroxy-alkene werden mittels Natrium/fl. Ammoniak mit guten Ausbeuten zu Alke-nen reduziert (Bd- V/lb, S. 626 f. u. Tab. S. 628). Dabei ist zu beachten, dafi nach dem Ver-fahren von Birch oft Allyl-Umlagerung eintritt. 

Oxidative cyclization of 5-hydroxy alkenes. Reaction of these substrates with Rc207 and a base (preferably 2,6-lutidinc) in CH2C12 at 25° provides 2-hydroxytctra-... 

Van Kuijk, F.J.G.M., Thomas, D.W., Stephens, R.J. and Dratz, E.A. (1986) Occurrence of 4-hydroxy-alkenals in rat tissues determined as pentafluorbenzyloxime derivatives by gas chromatography-mass spectrometry. Biochem. Biophys. Res. Commun. 139 144—149. 

Substituted furans have been prepared by acid-catalyzed cyclization of protected 4-hydroxy-alkenes of type (14), which are quite easily available from methoxy(phenylthio)methane both (Z)-and ( )-isomers of (14) gave the furan (Equation (16)) <83CL1909>. 

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