Hydroxyl compounds triols

The two main groups used as chain extenders are diamines and hydroxyl compounds. Triols are also used where some cross-linking is required. The choice of chain extender depends on the properties required and the process conditions. Diols are the most commonly used hydroxyl compound. In the normal course of events, diols provide good properties and processing speed with MDI-based prepolymers and diamines with TDI-terminated prepolymers. 

Products intermediate to the flexible and rigid foams may be obtained from castor oil (a trihydroxyl molecule), synthetic triols of moderate molecular weight and polyesters with a moderate amount of trifunctional hydroxyl compound in the strueture. Current practice, however, is to use tipped polyols of the type used for flexible foams with MDI. Semi-rigid foams are used for such purposes as crash pads, car steering wheels and packaging equipment. 

Di-t-butyl chromate and its pyridine adduct are suitable for large-scale oxidations of alcohols to ketones, thus cyclododecanol was converted into cyclododecanone (97 Alcohols are easily separated from non-hydroxylic compounds via their calcium chloride complexes. This method was used to separate cyclododecanone and cyclododecanol and is suitable for the separation of large quantities of material." All-cis-cyclododecane-l,5,9-triol was converted into the all-cis-tri-amine by tosylation, azide substitution, and reduction, and the amine acylated with 2,3-dimethoxybenzoyl chloride to give the tri-amide, an analogue of enterochelin. ... 

It may be noted here that castor oil is used as a hydroxyl-compound in the preparation of polyurethanes, particularly for coatings and adhesives. Castor oil is essentially a triol, being composed largely of glycerol triricinoleate (see Table 11.2). 

Hydroxy derivatives of silanes in which the hydroxyl groups are attached to a silicon atom are named by adding the suffices -ol, -diol, -triol etc., to the name of the parent compound. Examples are ... 

The next key step, the second dihydroxylation, was deferred until the lactone 82 had been formed from compound 80 (Scheme 20). This tactic would alleviate some of the steric hindrance around the C3-C4 double bond, and would create a cyclic molecule which was predicted to have a greater diastereofacial bias. The lactone can be made by first protecting the diol 80 as the acetonide 81 (88 % yield), followed by oxidative cleavage of the two PMB groups with DDQ (86% yield).43 Dihydroxylation of 82 with the standard Upjohn conditions17 furnishes, not unexpectedly, a quantitative yield of the triol 84 as a single diastereoisomer. The triol 84 is presumably fashioned from the initially formed triol 83 by a spontaneous translactonization (see Scheme 20), an event which proved to be a substantial piece of luck, as it simultaneously freed the C-8 hydroxyl from the lactone and protected the C-3 hydroxyl in the alcohol oxidation state. 

A magnesium enolate of 99 is susceptible to aldol condensation with 4-pentenal, and the crude product can be directly protected to give its ethyl carbonate 100. a-Hydroxylation of the carbonyl group yields the hydroxyl carbonate 101. Reduction of the carbonyl group generates a triol, and this compound can be simultaneously converted to carbonate 102. Swern oxidation of 102 gives ketone 103, which can be rearranged25 to produce lactone product 104 (Scheme 7-32). 

A series of compounds has been prepared where two of the hydroxyl linkages of the triol-series are replaced by nitro-groups. These are the hexammino-ju-dinitro-ol-dieobaltic salts.1... 

An alternate entry to the narciclasine class of alkaloids has provided access to compounds related to isonarciclasine (263) (Scheme 24). In the event, the aryla-tion of p-benzoquinone with diazonium salts derived from the aryl amines 250 and 251 yielded the aryl-substituted benzoquinones 252 and 253, respectively (146). The selective hydroxylation of 252 and 253 with osmium tetraoxide provided the corresponding m-diols 254 and 255. Catalytic hydrogenation of 254 and 255 using Pd/C or Raney Ni and subsequent lactonization gave the triols 256 and 257 together with small amounts of the C-2 a-epimers 258 and 259. Aminolysis of 256 and 257 afforded the corresponding racemic tetrahydrophen-anthridones 260 and 261, whereas similar treatment of the a-epimers 258 and 259 led to the formation of ( )-isolycoricidine (262) and ( )-isonarciclasine (263), respectively. 

Hydroxyl groups in partially substituted compounds may be transformed into halo, amino, oxo, deoxy, and other functional groups. Free 1,6-anhydrohexopyranoses199,200 and their aminodeoxy201,202 derivatives tend to form cationic and anionic complexes, in particular with l,6-anhydro-/J-D-allopyranose, which has a vicinal triol system in axial-equatorial-axial arrangement.200... 

Alternatively, synthesis of compound 215 (4-epimer of 208) started by initial inversion of the OH group at C-l of 207 (Scheme 27).35,96,99 101 Acid hydrolysis of 207 gave the triol 209 (100%), which was identified as its tetraacetate 210, whose allylic hydroxyl group was selectively sulfonylated with mesyl chloride to afford 211, which was then converted into the acetate 212 (65%). On treatment with an excess of sodium acetate in DMF, 212 afforded 213 (60%). Oxidation of 213 with osmium tetraoxide gave, after acetylation, 214 and 216. Furthermore, epoxidation of 213 gave a single spiro epoxide 214 (64%), which was transformed exclusively into 216 (83%)... 

To obtain acceptors with a free 3-OH, an approach exploiting the regioselec-tive opening of cyclic orthoesters was used. Debenzylation of 2 afforded the 2,3,4-triol 3, from which the 2,3-cyclic orthoester was formed. This was followed by acetylation of the 4-hydroxyl group to give a fully protected compound. Acidic opening of the orthoester then gave exclusively the 3-OH acceptor 4 (Scheme 3). 

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