4-Pentene-l,3-diol

The intramolecular oxidative earbonylation has wide synthetie applieation. The 7-lactone 247 is prepared by intramolecular oxycarbonylation of the alke-nediol 244 with a stoichiometric amount of Pd(OAc)2 under atmospheric pres-sure[223]. The intermediate 245 is formed by oxypalladation, and subsequent CO insertion gives the acylpalladium 246. The oxycarbonylation of alkenols and alkanediols can be carried out with a catalytic amount of PdCl2 and a stoichiometric amount of CuCb, and has been applied to the synthesis of frenolicin(224] and frendicin B (249) from 248[225]. The carbonylation of the 4-penten-l,3-diol 250, catalyzed by PdCl2 and CuCl2, afforded in the c -3-hydroxytetrahydrofuran-2-aeetie acid lactone 251[226J. The cyclic acetal 253 is prepared from the dienone 252 in the presence of trimethyl orthoformate as an accepter of water formed by the oxidative reaction[227]. 

Iodocyclization to hydroxy tetrahydrofurans. Cyclization of y,8-unsaturated alcohols to tetrahydrofurans (12, 254-256) can be directed by an allylic oxygen substituent, which also can increase the rate of cyclization. Thus derivatives of 4-pentene-l,3-diol undergo iodocyclization mainly to dr-3-hydroxy-2-iodomethylte-trahydrofurans. 

Oxycarbonylation of 4-pentene-l,3-diols. Oxycarbonylation of these diols (CO,NaOAc,CuCl2) catalyzed by PdCl2 provides the lactones of ds-2-(3-hydroxy-tetrahydrofuranyl)acetic acid. 

Catalytic asymmetric intramolecular hydrosilylation of dialkyl- and diarylsilyl ethers of bis(2-propenyl)methanol (245) catalyzed by (R, R)-DIOP-Rh or (R)-binap-Rh complex, followed by Tamao oxidation, gives (2S, 3R)-2-methyl-4-pentene-l,3-diol (247) with 71-93% ee and excellent syn selectivity (syn/anti = 95/5- > 99/1) (equation 96)249. The enantioselectivity of this reaction depends on the bulkiness of the silyl moiety, i.e. the bulkier the substituent, the higher is the enantiopurity of the product, except for the case of 2-MeCgH4 R = Me, 80% ee (binap-Rh) R = Ph, 83% ee (DIOP-Rh) R = 2-McC.fiI I4, 4% ee (DIOP-Rh) R = 3-MeC6H4, 87% ee (DIOP-Rh) R = 3,5-Me2C6H3, 93% ee (DIOP-Rh). This methodology is successfully applied to the asymmetric synthesis of versatile poly oxygenated synthetic intermediate 249 (equation 97)249. 

On the other hand, higher 1,2-asymmetric induction is observed for the cyclization of 5-aIkenols which bear an oxygenated function at C-4. Thus, treatment of 5-hexen-1,4-dioI (3) with phenyl-selenyl triflate in dichloromcthanc at —78 °C gives the corresponding tetrahydro-2/f-pyran 4 in 52% yield as a 91 9 (cis/trans) mixture. The preferential 2,3-cis relationship can be explained by analogy with the halocyclization of 4-pentene-l,3-diols (see Section 4.6.2.1.1.3.)19. 

Stereoselective alkoxycarbonylation with lactone formation is achieved in the intramolecular heterocarbonylation of 4-pentene-l,3-diols and 3-hydroxy-4-pentenoic acids57 - 59,97. 

Thermal rearrangement of 5 in toluene results in the same selectivity. The diastereomers 8 can be separated, and enantiomerically pure 4-penten-l, 3-diol has been prepared from (R)-9. The facial selectivity has been explained by unfavorable l,3-.yyn diaxial interactions in the case of si attack. 

Tamaru Y, Hojo M, Kawamura S, Sawada S, Yoshida Z (1987) Stereoselective intramolecular iodoetherification of 4-pentene-l,3-diols synthesis of cw-2-(iodomethnyl)-3-hydroxyte-trahydrofurans. J Org Chem 52 4062-4072x... 

That same year, Yoshida and colleagues demonstrated the oxidative carbonylation of 4-penten-l,3-diols. In the presence of PdCL (0.1 equiv), CuCL (3 equiv), NaOAc (3 equiv) and under CO (1 bar) at room temperature, lactones were achieved stereoselectively [59]. They also succeeded in finding optimal conditions for the oxidative carbonylation of 3-hydroxypent-4-enylamides to produce the... 

Tamaru Y, Kobayashi T, Kawamura S-1, Ochiai H, Hojo M, Yoshida Z-I. Palladium catalyzed oxycarbonylation of 4-penten-l,3-diols efficient stereoselective synthesis of cis 3-hydroxytetrahydrofuran 2-acetic acid lactones. Tetrahedron Lett. 1985 26 3207-3210. 

Hydroxylation of polyolefins by Milas reagent can be so arranged that only one double bond is affected e.g., cyclopentadiene gives a mixture of 3-cyclo-pentene-l,2-diol and 4-cyclopentene-l,3-diol.139,143 Another application of this method was the selective oxidation of / -carotene to vitamin-A aldehyde.144... 

Under these conditions saturated primary and secondary aliphatic and alicyclic alcohols are recovered essentially unchanged. This selectivity was illustrated impressively by conversion of Z-3-methyl-2-pentene-l,5-diol (4) by treatment with the complex (I) in methylene chloride briefly at - 20° and then at 0° for 1 hr. into the allylic monochloride (5), isolated in 87% yield. 

In this work we extend our study to the hydrogenation and isomerization of a series of a,p-unsaturated alcohols, such as 2-propen-l-ol (A2), (E -2-buten-l-ol (EB2), (" -2-penten-l-ol (ZP2), (E -2-penten-l-ol (EP2), (" -2-hexen-l-ol (ZH2), (E -2-hexen-l-ol (EH2), carried out in the presence of RhCl(PPh3)3, with and without triethylamine (NEts), at 303 K, using ethanol as solvent. The major targets of our research are to investigate the influence of the unsaturated alcohol structure on the product distribution and to verify the possibility of extending the results, previously obtained with (" -2-butene-1,4-diol, to other analogous substrates. 

Trimethyl-1 -Pentene Trimethylsilyl Chloride 3.6,9-Trioxaundecan-l, 11-Diol Tripropylene Tripropylene Glycol... 

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