2-Ene-l,4-diols

The palladium-promoted conversion of 1,3-dienes to pyrroles proceeds via 4-acetoxy-2-alkenylpalladium complexes (Scheme 50g) (81CC59), and a similar pathway may be involved in the palladium mediated reaction of but-2-ene-l,4-diol with primary amines to give A-substituted pyrroles (74CC931). 

Trost and co-workers have explored asymmetric transidon metal-catalyzed allylic alkyla-dons. Details on this subject have been well reviewed by Trost and others. With the use of asymmetric palladium-catalyzed desymmetrizadon of meso-2-ene-l,4-diols, cii -l,4-dibenzoy-loxy-2-cyclopentene can be converted to the enandometrically pure cii -4-rfirr-butoxycar-bamoyl-l-methoxycarbonyl-2-cyclopentene. The product is a usefid and general building block for synthesis of carbocyclic analogs of nucleosides as presented in Scheme 5.12. 

Finally, the nucleophile to a lithiated epoxide need not be the base originally used to generate it, or even one that has been externally added, but can be another lithiated epoxide. This disproportionation/carbenoid dimerization of (enantio-pure) lithiated epoxides provides 2-ene-l,4-diols (Scheme 5.33) [53]. Syntheses of D-mannitol and D-iditol in three steps from (S) -tritylglycidyl ether were achieved with this method. 

Iodotrimethylsilane formed in situ from the reaction of chlorotrimethylsilane and sodium iodide, also effects the conversion of 2-ene-l,4-diols to 1,3-dienes (equation 16)46. Allylic thionocarbonates on heating with triphenylphosphite undergo deoxygenation (Corey-Winter reaction) to generate olefins47. This procedure has been used for making hexatrienes (equation 17)47b. 

Replacing hex-3-ene with trans-1,4-dimethoxybut-2-ene resulted in slightly slower reactions, but gave comparable yields of cross-metathesis products. The desired reactions did not take place, however, when ris-but-2-ene-l,4-diol was used as the acyclic substrate. 

Bromo-l,4-dihydroxybutan-2-one 1,4-bisphosphate (31) has been prepared from the protected bromohydrin of cw-but-2-ene-l,4-diol.95 Nucleophiles rapidly displace bromide ion from (31), and the latter has been used as an affinity label for ribulose-bisphosphate carboxylase. In this case two sites are labelled in each enzyme molecule, the two molecules of (31) being linked to the enzyme by two different lysine residues.96... 

Kolbe oxidation of carboxylate ions to radicals with loss of carbon dioxide (p. 312). The latter process gives highest yields of dimeric product at a platinum anode and only monomeric products from oxidation of the radical centre at a carbon anode. Oxidation of butadiene in methanol containing benzoic acid, at a smooth platinum anode, gives 45 % of the but-3-ene-l,4-diol diester [45]. 

Reductive elimination from 2-ene-l,4-diol derivatives has been used to generate 1,3-dienes. Low-valent titanium generated from TiCl3/LiAlH4 can be used directly with the... 

Benzoate esters of 2-ene-l,4-diols undergo reductive elimination with sodium amal-... 

Ene-l,4-diols are transformed into furans by Dess-Martin period-inane.150... 

Z)-But-2-ene-l,4-diol.24 But-2-yne-l,4-diol (20g) is dissolved in methanol (350ml) and hydrogenated at atmospheric pressure in the presence of 0.5 per cent palladium-on-calcium-carbonate (2.0 g). After 24 hours one equivalent of hydrogen (5650 ml) will be absorbed. The catalyst is then separated and the filtrate distilled, giving (Z)-but-2-ene-l,4-diol as a colourless oil (15.7g, 77%), b.p. 134-135 °C/15 mmHg, n 5 1.4716. The product forms a dibenzoate (prisms from aqueous methanol), m.p. 69-70 °C. 

Dienes. Low-valent titanium (TiCl3/LiAlH4 = 2 1) reacts with 2-ene-l,4-diols to give 1,3-dienes by a 1,4-reductive elimination.2 Examples ... 

Noyori and colleagues investigated the ring opening of unsaturated mono- and bicyclic endoperoxides catalyzed by 5-10 mol% of Pd(PPh3)4 [226, 227]. Similarly to the cobalt-catalyzed reactions, (Z)-4-hydroxy enones resulted as the main products, which were accompanied by (Z)-2-ene-l, 4-diols and diepoxides. The latter are formed as the major products under either ruthenium or cobalt catalysis (see Part 2, Sects. 3.5 and 5.8). Both two-electron and radical mechanisms were considered for this transformation. Saturated bicyclic endoperoxides gave mixtures of cyclic 4-hydroxy ketones and 1,4-diols and their formation may be a result of a radical process [227, 228]. 

The reaction of terminal epoxides with hindered lithium amide bases followed by organometallic reagents generates alkenes <2004JA12250>. Related reactions are the formation of enamines <2004JA6870> from terminal epoxides, 2-ene-l,4-diols from terminal epoxides <20050L2305>, and allylamines from amino epoxides <20060L349>. 

The compound (54) has been enzymatically converted into a phosphorylated derivative of (E)-2-methylbut-2-ene-l,4-diol, which most probably represents a novel intermediate in the methylerythritol phosphate pathway of isoprenoid biosynthesis. The use of a photolabile acetal protecting group enables the synthesis of glycoaldehyde di-, and triphosphates (55) and (56) respectively. 

A total synthesis of 1,3-dideoxynojirimycin starting from cyclopentadiene was proposed by Johnson et al. [206]. Photooxidation of cyclopentadiene and reductive workup with thiourea generates c/ -cyclopent-2-ene-l,4-diol, which is monoacylated with high enantioselectivity (>99% ee) with isoprenyl acetate and Candida antarctica lipase B (Novo Nordisk SP 435) to give 461. After silylation of 461 and subsequent treatment with KOH and oxidation, enantiomerically pure enone 462 is obtained [207]. 

Using this method, synthesis of functionalized substituted cyclopropanes can be achieved via nucleophilic alkylation of the monoacetates of but-2-ene-l,4-diols 18 with malonates (and similar stabilized) carbanions in the presence of a palladium(0) catalyst. Subsequent acylation of the second hydroxyl function and subsequent treatment with base in the presence of the palladium(0) catalyst leads to intramolecular nucleophilic alkylation. This method and similar conversions have been applied to numerous other cyclopropane ring constructions. - - ... 

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