Diol catalysts

Toda et al carried out a pioneering work in the area of chiral recognition by a,a,a a -tetraaryl-l,3-dioxolane-4,5-dimethanol (TADDOL) derivative. They found 

The acceleration of the reaction by hydrogen bonding has been studied theoretically [136]. DFT calculations, at the B3LYP/6-31G level, revealed the hydrogen bonding formation of chloroform. 

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In the catalytic system shown in Scheme 9, a hydrogen bond between one hydroxy function of the diol catalyst and the carbonyl group of the substrate is regarded as the driving force of catalysis. Here, the spatial orientation of the bulky a-1-naphthyl substituents of the TADDOL (a,a,a, a -tetraaryl-l,3-dioxolan-4,5-dimethanol) scaffold generates the chiral environment controlling the enantioselectivity of the reaction. 

Entry Diol Catalyst Inherent Viscosity (dl/g) Melt Index (g/10 min)... 

Microcellular polyurethanes for shoe soling are of both the polyester and polyether types. Polyester types were developed first and owing to their generally superior mechanical properties they tend to be used in the thinner sole, high quality section of the market. Such polyester systems are usually based on quasi-prepolymers (made from part of the polyester and the MDI) and a resin blend made up of the rest of the polyester, the chain extender (usually butane diol), catalysts, surfactants and water to produce carbon dioxide to blow the foams. The use of a quasi-prepolymer enables the two... 

I n this chapter, we wish to discuss the recent advancements in chiral Bronsted acid catalysis. We will focus chiefly on (i) thiourea catalysts [55], (ii) guanidium salts (protonated amine catalysts), (iii) diol catalysts, and (iv) phosphoric acids [56]. The first three catalysts are classified as neutral or weak Bronsted acids, which may be called hydrogen bond catalysts [57]. In contrast, phosphoric acids, being stronger acids, are Bronsted acid catalysts in a narrow sense (Figure 2.9). 

Table 5.3 Screening of various diol/Ti/diol catalyst combinations in the ring-opening reaction of 10 with benzylamine 11a.

Prepared by heating ammonium mucate, or from butyne-l,4-diol and ammonia in the presence of an alumina catalyst. The pyrrole molecule is aromatic in character. It is not basic and the imino-hydrogen atom can be replaced by potassium. Many pyrrole derivatives occur naturally, e.g. proline, indican, haem and chlorophyll. 

A highly diastereoselective alkcnylation of c/s-4-cyclopentene-l,3>diols has been achieved with 0-protected (Z)-l-iodo-l-octen-3-ols and palladium catalyst (S. Torii, 1989). The ( )-isomers yielded 1 1 mixtures of diastcrcomcric products. The (Z)-alkenylpalladium intermediate is thought to undergo sy/i-addition to the less crowded face of the prochiral cyclopentene followed by syn-elimination of a hydropalladium intermediate. 

The first practical method for asymmetric epoxidation of primary and secondary allylic alcohols was developed by K.B. Sharpless in 1980 (T. Katsuki, 1980 K.B. Sharpless, 1983 A, B, 1986 see also D. Hoppe, 1982). Tartaric esters, e.g., DET and DIPT" ( = diethyl and diisopropyl ( + )- or (— )-tartrates), are applied as chiral auxiliaries, titanium tetrakis(2-pro-panolate) as a catalyst and tert-butyl hydroperoxide (= TBHP, Bu OOH) as the oxidant. If the reaction mixture is kept absolutely dry, catalytic amounts of the dialkyl tartrate-titanium(IV) complex are suflicient, which largely facilitates work-up procedures (Y. Gao, 1987). Depending on the tartrate enantiomer used, either one of the 2,3-epoxy alcohols may be obtained with high enantioselectivity. The titanium probably binds to the diol grouping of one tartrate molecule and to the hydroxy groups of the bulky hydroperoxide and of the allylic alcohol... 

Efficient acetalization of alkenes bearing various EWG with an optically active 1.3-diol 72 proceeds smoothly utilizing PdCN, CuCI. and O2 in DME to give the 1,3-dioxane 73[113], Methacrylamide bearing 4-t-butyloxazolidin-2-one 74 as a chiral auxiliary reacts with MeOH in the presence of PdCE catalyst... 

The carbonylation of 2-methyl-3-butyn-2-oI (50) in benzene gives teraconic anhydride (51). Fulgide (53) (a dimethylenesuccinic anhydride derivative), which is a photochromic compound, can be prepared by the carbonylation of 2,5-dimethyl-3-hexyne-2,5-diol (52)[21], The reaction proceeds under milder conditions when PdlOAc) is used as a catalyst in the presence of iodine [23],... 

Conversion to dialkyl ethers (Sec tion 15 7) On being heated in the presence of an acid catalyst two molecules of a primary alcohol combine to form an ether and wa ter Diols can undergo an intramo lecular condensation if a five membered or six membered cyclic ether results... 

Many of the reactions listed at the beginning of this section are acid catalyzed, although a number of basic catalysts are also employed. Esterifications are equilibrium reactions, and the reactions are often carried out at elevated temperatures for favorable rate and equilibrium constants and to shift the equilibrium in favor of the polymer by volatilization of the by-product molecules. An undesired feature of higher polymerization temperatures is the increased probability of side reactions such as the dehydration of the diol or the pyrolysis of the ester. Basic catalysts produce less of the undesirable side reactions. 

An early attempt to hydroformylate butenediol using a cobalt carbonyl catalyst gave tetrahydro-2-furanmethanol (95), presumably by aHybc rearrangement to 3-butene-l,2-diol before hydroformylation. Later, hydroformylation of butenediol diacetate with a rhodium complex as catalyst gave the acetate of 3-formyl-3-buten-l-ol (96). Hydrogenation in such a system gave 2-methyl-1,4-butanediol (97). 

Heating with cuprous chloride in aqueous hydrochloric acid isomerizes 2-butene-l,4-diol to 3-butene-l,2-diol (98)] Various hydrogen-transfer catalysts isomerize it to 4-hydroxybutyraldehyde [25714-71-0] (99), acetals of which are found as impurities in commercial butanediol and... 

Treatment with acidic catalysts dehydrates i j -butenediol to 2,5-dihydrofuran [1708-29-8], C H O (100). Cupric (101) or mercuric (102) salts give 2,5-divinyl-l,4-dioxane [21485-51-8], presumably via 3-butene-l,2-diol. 

Reduction. Hydrogenation of dimethyl adipate over Raney-promoted copper chromite at 200°C and 10 MPa produces 1,6-hexanediol [629-11-8], an important chemical intermediate (32). Promoted cobalt catalysts (33) and nickel catalysts (34) are examples of other patented processes for this reaction. An eadier process, which is no longer in use, for the manufacture of the 1,6-hexanediamine from adipic acid involved hydrogenation of the acid (as its ester) to the diol, followed by ammonolysis to the diamine (35). 

CycHc carbonates are made by treating 1,2-diols with dialkyl carbonates using an alkyl ammonium and tertiary amine catalyst. The combination of propylene glycol and dimethyl carbonate has been reported to result in a 98% yield of propylene carbonate (21). 

Acetals andKetals. Acetals of 1,3-diols are prepared by refluxing the diol with the aldehyde in the presence of an acid catalyst, even in an aqueous medium. The corresponding ketals are more difficult to prepare in aqueous solution, but cycHc ketals of neopentyl glycol, eg, 2-butyl-2-ethyl-5,5-dimethyl-l,3-dioxane (3), can be prepared if the water of reaction is removed azeotropicaHy (34). 

Ethynylation. Base-catalyzed addition of acetylene to carbonyl compounds to form -yn-ols and -yn-glycols (see Acetylene-DERIVED chemicals) is a general and versatile reaction for the production of many commercially useful products. Finely divided KOH can be used in organic solvents or Hquid ammonia. The latter system is widely used for the production of pharmaceuticals and perfumes. The primary commercial appHcation of ethynylation is in the production of 2-butyne-l,4-diol from acetylene and formaldehyde using supported copper acetyHde as catalyst in an aqueous Hquid-fiHed system. 

Acetylene is condensed with carbonyl compounds to give a wide variety of products, some of which are the substrates for the preparation of families of derivatives. The most commercially significant reaction is the condensation of acetylene with formaldehyde. The reaction does not proceed well with base catalysis which works well with other carbonyl compounds and it was discovered by Reppe (33) that acetylene under pressure (304 kPa (3 atm), or above) reacts smoothly with formaldehyde at 100°C in the presence of a copper acetyUde complex catalyst. The reaction can be controlled to give either propargyl alcohol or butynediol (see Acetylene-DERIVED chemicals). 2-Butyne-l,4-diol, its hydroxyethyl ethers, and propargyl alcohol are used as corrosion inhibitors. 2,3-Dibromo-2-butene-l,4-diol is used as a flame retardant in polyurethane and other polymer systems (see Bromine compounds Elame retardants). 

Diol Components. Ethylene glycol (ethane 1,2-diol) is made from ethylene by direct air oxidation to ethylene oxide and ring opening with water to give 1,2-diol (40) (see Glycols). Butane-1,4-diol is stiU made by the Reppe process acetylene reacts with formaldehyde in the presence of catalyst to give 2-butyne-l,4-diol which is hydrogenated to butanediol (see Acetylene-DERIVED chemicals). The ethynylation step depends on a special cuprous... 

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