Pentanediol, reactions

Trimethylene dibromide (Section 111,35) is easily prepared from commercial trimethj lene glycol, whilst hexamethylene dibromide (1 O dibromohexane) is obtained by the red P - Br reaction upon the glycol 1 6-hexanediol is prepared by the reduction of diethyl adipate (sodium and alcohol lithium aluminium hydride or copper-chromium oxide and hydrogen under pressure). Penta-methylene dibromide (1 5-dibromopentane) is readily produced by the red P-Brj method from the commercially available 1 5 pentanediol or tetra-hydropyran (Section 111,37). Pentamethylene dibromide is also formed by the action of phosphorus pentabromide upon benzoyl piperidine (I) (from benzoyl chloride and piperidine) ... 

Vinyl ethers and a,P unsaturated carbonyl compounds cyclize in a hetero-Diels-Alder reaction when heated together in an autoclave with small amounts of hydroquinone added to inhibit polymerisation. Acrolein gives 3,4-dihydro-2-methoxy-2JT-pyran (234,235), which can easily be hydrolysed to glutaraldehyde (236) or hydrogenated to 1,5-pentanediol (237). With 2-meth5lene-l,3-dicarbonyl compounds the reaction is nearly quantitative (238). 

Esters. The monoisobutyrate ester of 2,2,4-trimethyl-1,3-pentanediol is prepared from isobutyraldehyde ia a Tishchenko reaction (58,59). Diesters, such as trimethylpentane dipelargonate (2,2,4-trimethylpentane 1,3-dinonanoate), are prepared by the reaction of 2 mol of the monocarboxyhc acid with 1 mol of the glycol at 150—200°C (60,61). The lower aUphatic carboxyHc acid diesters of trimethylpentanediol undergo pyrolysis to the corresponding ester of 2,2,4-trimethyl-3-penten-l-ol (62). These unsaturated esters reportedly can be epoxidized by peroxyacetic acid (63). 

The by-products of these reactions are sulfides. The sulfide formed in the synthesis of 2-mercaptoethanol, 3-thia-l,5-pentanediol (thiodiglycol), has a variety of uses ranging from lubricant additive intermediates to textile finishing. 

The reaction products of TYZOR TPT with 2—4 moles of 1,3-diols having two to three alkyl substituents, such as 2,2,4-trimethyl-l,3-pentanediol, gives complexes that could be used as cross-linking agents for hydroxy group containing powdered lacquer resins (76). 

Many commercially important isobutyraldehyde derivatives are prepared through aldol and/or Tischenko condensation reactions. For example, isobutyraldehyde undergoes the aldol reaction to form isobutyraldol (2,2,4-trimethyl-3-hydroxypentanal [918-79-6]) which, when hydrogenated, gives 2,2,4-trimethyl-1,3-pentanediol (TMPD) [144-19-4],... 

In this model, the intermediacy of a monomeric zinc species is postulated. To support this assumption, an examination of the effect of stoichiometry and solvent in cyclopropanation involving the 2,4-pentanediol auxiliary was preformed [59]. In the initial reaction protocol, a large excess of both diethylzinc and diiodo-methane is employed. Such excessive conditions are justified on account of the instability of the zinc carbenoid under the reaction conditions. To minimize the un-... 

On the other hand, Davies5 , studying the reaction of adipic add with 1,5-pentanediol in diphenyl oxide or diethylaniline found an order increasing slowly from two with conversion. From this result he concluded that Flory s1,252-254> and Hinshelwood s240,241 interpretations are erroneous. Two remarks must be made about the works of Davies5 experimental errors relative to titrations are rather high and kinetic laws are established for conversions below 50%. Under such conditions the accuracy of experimental determinations of orders is rather poor. 

Chiral acetals/ketals derived from either (R,R)- or (5,5 )-pentanediol have been shown to offer considerable advantages in the synthesis of secondary alcohols with high enantiomeric purity. The reaction of these acetals with a wide variety of carbon nucleophiles in the presence of a Lewis acid results in a highly diastereoselective cleavage of the acetal C-0 bond to give a /1-hydroxy ether, and the desired alcohols can then be obtained by subsequent degradation through simple oxidation elimination. Scheme 2-39 is an example in which H is used as a nucleophile.97... 

From a practical point of view, the catalytic asymmetric hydrogenation of the corresponding diones will be the preferred method if high yields and high enantioselectivity can be ensured. Recently, over 98% yield with more than 99% ee has been achieved by optimizing the reaction conditions.64 For example, asymmetric hydrogenation of 2,4-pentanedione catalyzed by Ru-BINAP complex in the presence of hydrochloric acid gave 2,4-pentanediol in more than 95% yield and over 99% ee (Scheme 6-29).64... 

As depicted in Fig. 6, syntheses of enantiomerically pure 116 and 117 have been carried out [236]. Lipase AK-catalysed asymmetric acetylation of meso-2,4-dimethyl-1,5-pentanediol A yielded (2R,4S)-5-acetoxy-2,4-dimethylpen-tanol B. Protection of the free hydroxy group as the terf-butyldimethylsilyl (TBS) ether, saponification of the acetate, and oxidation furnished the aldehyde C. Reaction of C with ethylmagnesium bromide gave a diastereomeric mixture of the corresponding secondary alcohols which could be resolved by asym-... 

The same group also demonstrated an efficient, two-step asymmetric synthesis of (S)-2-phenylpiperidine as an extension of the N-heterocycUzation of primary amines with diols the results are illustrated in Scheme 5.25. First, the reaction of enantiomerically pure (R)-l-phenylethylamine and 1-phenyl-1,5-pentanediol was conducted to produce a diastereomeric mixture of the corresponding N-(l-phenyl-ethyl)-2-phenylpiperidines 32 and 33 with 92% diastereomeric excess (de). Hydrogenation of this diastereomeric mixture of 32 and 33 with Pd/C catalyst then gave (S)-2-phenylpiperidine in 96% yield (78% ee). 

The use of tartrate esters was an obvious place to start, especially since both enantiomers are readily available commercially and had already found widespread application in asymmetric synthesis (Figure 11) (e.g.. Sharpless asymmetric epoxidation).23.24 Reagents 36-38 are easily prepared and are reasonably enantioselective in reactions with achiral, unhindered aliphatic aldehydes (82-86% ee) typical results are given in Figure 12.3c,h Aromatic and a,p-unsaturated aldehydes, unfortunately, give lower levels of enantioselection (55-70% e.e.). It is also interesting to note that all other C2 symmetric diols that we have examined (2,3-butanediol, 2,4-pentanediol, 1,2-diisopropylethanediol, hydrobenzoin, and mannitol diacetonide, among others) are relatively ineffective in comparison to the tartrate esters (see Table ll).25... 

ANTI-SELECTIVE BORON-MEDIATED ASYMMETRIC ALDOL REACTION OF CARBOXYLIC ESTERS SYNTHESIS OF (2S, 3R)-2,4-DIMETHYL-1,3-PENTANEDIOL... 

Wu et al. have studied adsorption and reaction of 2-iodoethanol [177] and acetaldehyde [178] on Ag(lll). Doubovaet al. [179] have studied adsorption of amyl alcohol on Ag(lll) electrodes in 0.05 M KGIO4 solutions and explained the observed differences and inconsistencies in the light of the applied experimental technique (e.g. the role of ac frequency) and the electrode surface preparation procedure. Generally, amyl alcohol was adsorbed less on Ag(lll) than on Hg. The electron-induced surface reactions of methyl formate [180] and methanol [181] on Ag(l 11) have been studied by Schwaner and White. Foresti et al. [182] have investigated electrochemically, adsorption of 1,5-pentanediol on the Ag(lll) and Ag(llO) faces. 

N-Heterocyclization.1 1,5-Pentanediol reacts with primary amines at 150-180° in the presence of a ruthenium catalyst to form N-substituted piperidines. For the reaction with aromatic amines RuC I QHs) is the catalyst of choice. On the other hand, the most effective catalyst for the reaction with aliphatic amines is RuC13 combined with either tributylphosphine or triethylphosphine. 

Chromium carbene complexes, 82 Methyl acrylate, 183 (2R,4R)-Pentanediol, 237 Titanium(IV) chloride, 304 Nitroaldols Nitromethane, 199 Intramolecular reactions Methyl acrylate, 183 Other aldol-type reactions Bis(2-pyridinethiolato)tin(II), 40 Alkoxycarbonylation (see Carboalkoxy-lation)... 

Preparation of Poly (propylene ether) Polyols. The polymerization of propylene oxide with zinc hexacyanocobaltate complexes in the presence of proton donors results in the production of low-molecular-weight polymers. Table V shows the variety of types of compounds that have been found to act this way. Since these compounds end up in the polymer chains, it seems reasonable to call them chain initiators. Thus, in essence, each of these compounds is activated by the catalyst to react with propylene oxide to form a hydroxylpropyl derivative. Thereafter, the reaction continues on the same basis, with the proton of the hydroxyl group reacting with further propylene oxide. This sequence is shown here with 1,5-pentanediol as the initiator. The hydroxyl... 

---