Symmetrical Diols Research Articles

Synthesis of metal complexes of polyalkylene(arylene) phosphorous amides

Reactions of phosphorous triamides with symmetrical diols in equimolar ratio were studied. These reactions result in formation of unique poly(oligo)amidophosphorous systems. The products obtained are used as ligands for the synthesis of metal complexes of a new type.

Partial reduction of pyrroles: application to natural product synthesis

The partial reduction of N-Boc pyrroles has been explored giving stereoselective routes to disubstituted pyrrolines in good yields and with excellent diastereoselectivities. A novel methodology has been developed to carry out reductive aldol reactions on 2-substituted N-Boc pyrroles; use of aldehydes under reductive aldol conditions gave the anti aldol product in good selectivity. This chemistry was used as the key transformation in a synthesis of omuralide, which was achieved in 13 steps and 14% overall yield. We also report a methodology for selectively forming either cis or trans 2,5-disubstituted pyrrolines via a partial reduction of an electron-deficient N-Boc pyrrole. The trans pyrroline formed using this route was utilized in the syntheses of the polyhydroxylated pyrrolizidine natural products hyacinthacine A1 and 1-epiaustraline. Further investigation has led to the development of routes to enantiopure substituted pyrroline compounds. This has been achieved via a chiral protonation approach using easily accessible chiral acids, such as ephedrine and oxazolidinones, to quench enolates formed during the partial reduction process. Alternatively, enzymatic desymmetrization of symmetrical diol compounds formed from the partial reduction products of substituted pyrroles is also reported. This leads to formation of both enantiomers of 2,2- and 2,5-disubstituted N-Boc pyrrolines in excellent ee and yields.

A highly selective and efficient acetylation of alcohols and amines with acetic anhydride using NaHSO 4·SiO 2 as a heterogeneous catalyst

Treatment of alcohols and amines (aliphatic and aromatic) with acetic anhydride at room temperature using NaHSO 4·SiO 2 as a heterogeneous catalyst affords the corresponding acetates in excellent yields. The method is highly chemoselective—alcoholic hydroxyl group can be protected while phenolic hydroxyl group remains intact and the amine group can be acetylated in the presence of hydroxyl. Symmetrical diols produced only the monoacetates. The method has been applied for the preparation of venkatasin, a natural coumarino-lignan and of Baylis–Hillman acetates.

Chiral Diols: A New Class of Additives for Direct Aldol Reaction Catalyzed by l-Proline

Nine C2 symmetric diols have been examined as additives in the L-proline-catalyzed direct aldol reaction with significant improvement in enantioselectivity, conversion efficiency, and yield. Loading of 1 mol % of (S)-BINOL leads to the desired products in up to 98% ee and 90% yield. A transition state is proposed.

Syntheses and Applications of C2‐Symmetric Chiral Diols

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Highly Efficient Synthesis of Enantiopure Diacetylated C2‐Symmetric Diols by Ruthenium‐ and Enzyme‐Catalyzed Dynamic Kinetic Asymmetric Transformation (DYKAT)

Highly efficient synthesis of enantiopure diacetates of 2,4-pentanediol and 2,5-hexanediol starting from commercially available mixtures of the diols (dl/meso approximately 1:1) has been realized by combining a fast ruthenium-catalyzed epimerization with an enzymatic transesterification. The in situ coupling of these two processes produces the diacetates in high yield in >99 % enantiomeric excess.

1,1'-(Ethane-1,2-diyl)dipyridinium bistribromide (EDPBT) as a recyclable catalyst for acylation

Ethane-1,2-diyl)dipyridinium bistribromide (EDPBT) catalyzes the acylation of structurally diverse alcohols, amines, thiols, and phenols with a variety of aliphatic and aromatic anhydrides. Steric factors in substrates as well as anhydrides and solvent play significant role during the formation of acylates. Chemoselective mono acetylation of symmetrical diols, primary hydroxy group over secondary and phenolic group and amines over phenols has been achieved. The compatibility of the protocol has been shown by the survival of different acid sensitive functionalities under the present reaction condition. The solvent, acetone, reacts with EDPBT giving bromoacetone and HBr, thus suppressing the bromination of substrates otherwise amenable to bromination. The reagent EDPBT being devoid of phase transfer property and owing to the high solubility of its precursor 1,1'-(ethane-1,2-diyl)dipyridinium dibromide (EDPDB) in water, it was possible to isolate pure acylates by an aqueous work-up circumventing the need for further purification. The process is superior owing to the recyclability of the reagent. The spent reagent can be recovered, regenerated, and reused without any significant loss.

Convenient tetrahydropyranylation of alcohols and phenols by catalytic ferric sulfate hydrate (Fe2(SO4)3·xH2O)

Ferric sulfate hydrate (Fe2(SO4)3·xH2O) is found to be an efficient heterogeneous catalyst for the tetrahydropyranylation of alcohols and phenols at ambient or near ambient temperature. In addition, selective monotetrahydropyranylation of symmetrical diols is achieved under similar conditions. The deprotection of THP ether and direct transformation of THP ether to the corresponding acetate by Fe2(SO4)3·xH2O is also studied. The simplicity of manipulation, mild conditions, reusable catalyst, good selectivity, and environment benign characters make this method a good alternative way for the THP protection of alcohols.Key words: tetrahydropyranylation, selective monotetrahydropyranylation, ferric sulfate hydrate, green chemistry.

Double helical self-assembly in a C2h symmetric diol monohydrate: A study of the cooperativity between O–H⋯O and C–H⋯π interactions

A C2h symmetric diol monohydrate exhibits a double helical self-assembly in the solid state. The supramolecular architecture reveals an interesting cooperativity between the O–H⋯O hydrogen bonds, linking the water and diol molecules, and the C–H⋯π interactions, joining the tetrahedrally disposed molecules of the diol in the double helical structure. The role of the molecular symmetry of the diol in the observed crystal packing has been analysed through complementary examples.

Direct Organocatalytic Asymmetric α‐Hydroxymethylation of Ketones and Aldehydes.

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Direct organocatalytic asymmetric α-hydroxymethylation of ketones and aldehydes

Direct organocatalytic asymmetric α-hydroxymethylation of ketones and aldehydes with formaldehyde has been developed, which furnished the corresponding α-hydroxymethylated adducts with high chemo- and enantioselectivity. The reaction is catalyzed by proline derivatives and is a simple method for the enantioselective synthesis of α-hydroxymethylated ketones and aldehydes, and C-2 symmetric diols.

Studies on Novel Synthetic Methodologies. Part 30. Selective Monoacetylation of Symmetrical Diols and Selective Monodeacetylation of Symmetrical Diacetates Using HY‐Zeolite as Reusable Heterogeneous Catalyst.

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Curing and pyrolysis of cresol novolac epoxy resins containing [2‐(6‐oxido‐6H‐dibenz(c,e)(1,2)oxaphosphorin‐6‐yl)‐1,4‐naphthalenediol

AbstractThis study investigates the curing kinetics, thermal properties and decomposition kinetics of cresol novolac epoxy (CNE) with two curing agents, 2‐(6‐oxido‐6H dibenz(c,e)(1,2) oxaphosphorin‐6‐yl)‐1,4‐benzenediol (ODOPN), and phenol novolac (PN). In comparison with the conventional PN system, introducing ODOPN, a phosphorus‐containing bulky pendant group, into CNE increases Tg by 33°C, char yield from 30% to 38%, and LOI from 22 to 31. The DSC curing study reveals that the Ea of the CNE/ODOPN epoxy can be obtained by Kissinger's method. The resulting Ea values indicate that the catalytic effect of EMI is insignificant on CNE/ODOPN but is marked on CNE/PN, whose Ea was reduced from 131.5 to 75.6 KJ/mole. This result may be caused by the fact that the symmetric diol attached to the 1 and 4 positions of the naphthalene ring in ODOPN sets up a steadily resonating structure and inhibits the catalytic action. Further investigating the conversion ratio with curing temperature yielded experimental data that agreed closely with Kaiser's model. The orders of the autocatalyzed reaction, m, and the crosslinking reaction, n, are close to 0.5 and 1.0, respectively, independently of the scan rate. Finally, the TGA decomposition study by Ozawa's method demonstrates that the mean Ea declines with the phosphorus content, because the easy decomposition of the phosphorus compound in the initiation stage facilitates the formation of an insulating layer. However, results in this study further reveal an increasing tendency for Ea with decomposition conversion for an ODOPN/PN mixture with the ODOPN content of over 50%, probably because of the retardation of gas diffusion by the insulating layer of phosphorus compound.

Synthesis of the Marine Compound (2R,5Z,9Z)-2-Methoxyhexacosa-5,9-dienoic Acid via a Lipase-Catalyzed Resolution and a Novel O-Alkylation Protocol

The title compound has been synthesized by a facile route starting from 4-pentyn-1-ol. The enantioselectivity was attained by a strategy involving a lipase-catalyzed acetylation of a solid-phase immobilized long chain α-hydroxy acid. Another important feature of the synthesis was the formulation of an efficient HgO-catalyzed O-methylation of the α-hydroxy acids which proceeded without any racemization. The alkylation protocol was also highly efficient for selective mono-methylation/benzylation of symmetrical diols.

Chemoselective tetrahydropyranylation of alcohols and phenols using polystyrene supported aluminium chloride as a catalyst

A simple, efficient and highly chemoselective method for tetrahydropyranylation of alcohols and phenols has been developed by their reaction with 3,4-dihydro-2 H-pyran at room temperature in the presence of a catalytic amount of polystyrene supported AlCl 3. The method is also highly selective for monoprotection of symmetrical diols.

Oxidation of Monotetrahydropyranylated Short‐Chain Symmetrical Diols.

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Preparation of Monotetrahydropyranylated Short‐Chain Symmetrical Diols.

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Autocatalytic asymmetric reduction of 2,6-diacetylpyridine.

[reaction: see text] We report here that the C(2)-symmetric diol 2,6-bis(1-hydroxyethyl)pyridine (2) can effect chiral-catalyzed reduction of 2,6-diacetylpyridine (1) and produce more of the diol (2) with the same configuration in an enantiomerically enriched form. The two carbonyl functionalities of (1) are reduced in 90% conversion to produce the enantio-enriched C(2)-symmetric diol (40% ee, 47% de) using zinc trifluoromethanesulfonate and a catalytic amount of the chiral C(2)-symmetric diol (2).

Oxidation of Monotetrahydropyranylated Short-Chain Symmetrical Diols

The free hydroxyl functions of monotetrahydropyranylated three- to five-carbon symmetrical primary diols are oxidized to aldehydes, without cleavage of the protective group, by using pyridinium dichromate in CH2Cl2 and anhydrous MgSO4 as a water scavenger. The oxidation procedure is improved for these specific compounds since over oxidation to carboxylic acids and formation of dimeric esters are suppressed.

Preparation of Monotetrahydropyranylated Short-Chain Symmetrical Diols

Efficient and robust methods for the monoprotection of 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol as THP ethers have been developed. The preparation of 4-(tetrahydro-pyran-2-yloxy)-butan-1-ol from 1,4-butanediol and 5-(tetrahydro-pyran-2-yloxy)-pentan-1-ol from 1,5-pentanediol was accomplished using a two-phase system composed of CH2Cl2, 3,4-dihydro-2H-pyran, and aqueous 0.1 N HCL. Preparation of 3-(tetrahydro-pyran-2-yloxy)-propan-1-ol from 1,3-propanediol was accomplished using a water-free biphasic mixture composed of 1,3-propanediol, catalytic pyridinium p-toluenesulfonate, 3,4-dihydro-2H-pyran, and 25% ether in hexane. The compounds are very useful three- to five-carbon homologating agents.