Rearrangements glycols

Systematic investigation of the reaction conditions of the glycolate rearrangement shows that inverse addition of lithium diisopropylamide to a solution of the glycolate ester in tetrahydro-furan at — 78 °C followed by immediate addition of chlorotrimcthylsilanc is more advantageous, e.g., formation of 4493. 

Polyether Polyols. Polyether polyols are addition products derived from cyclic ethers (Table 4). The alkylene oxide polymerisation is usually initiated by alkah hydroxides, especially potassium hydroxide. In the base-catalysed polymerisation of propylene oxide, some rearrangement occurs to give aHyl alcohol. Further reaction of aHyl alcohol with propylene oxide produces a monofunctional alcohol. Therefore, polyether polyols derived from propylene oxide are not truly diftmctional. By using sine hexacyano cobaltate as catalyst, a more diftmctional polyol is obtained (20). Olin has introduced the diftmctional polyether polyols under the trade name POLY-L. Trichlorobutylene oxide-derived polyether polyols are useful as reactive fire retardants. Poly(tetramethylene glycol) (PTMG) is produced in the acid-catalysed homopolymerisation of tetrahydrofuran. Copolymers derived from tetrahydrofuran and ethylene oxide are also produced. 

R)-Pantolactone is also prepared in a sequence involving Claisen rearrangement of the chiral glycolate (24), although with poor enantioselectivity... 

Glycol and o -hydroxy acid cleavage Oxidative decarboxylation Oxidative rearrangement of olefins... 

The third approaeh to synthetic polymers is of somewhat less commereial importance. There is in fact no universally accepted deseription for the route but the terms rearrangement polymerisation and polyaddition are commonly used. In many respects this process is intermediate between addition and condensation polymerisations. As with the former teehnique there is no moleeule split out but the kinetics are akin to the latter. A typical example is the preparation of polyurethanes by interaction of diols (di-alcohols, glycols) with di-isocyanates Figure 2.7). 

Recently, in extending the reaction to aliphatic glycols, Ghera observed that p-nitrobenzoate esters gave better results than acetates, and that zinc acetate could be substituted for activated zinc. He has proposed that the rearrangement is a heterogeneous catalytic process, with the zinc acting as a Lewis acid ... 

Base catalyzed pinacol rearrangement of vicinal m-glycol monotosylates is a simple and useful general method for preparing perhydroazulenes. Thus, treatment of cholestane-5a,6a-diol 6-tosylate (115a) with either one mole-equivalent of potassium t-butoxide in f-butanol at 25° or with calcium carbonate in dimethylformamide at 100° gives a quantitative yield of 10(5 6/5H)... 

Studies by Levisalles and Tkatchenko on the mechanism and stereochemistry of the steroidal benzilic rearrangement have demonstrated that the configuration of the product obtained in about 85 % yield from 5a-cholestane-3,4-dione (27) is as shown (28). When redistilled ethylene glycol mono-... 

Nelson finds that when ascaridol sutlers rearrangement, cither by healing or by treatment with ferrous snlpbate, there are Iwo other bodies formed besides the glycol described by Schimmel. One of these is also a glyco), which he terms /I-glycoI, to distinguish it from the other one, It has the formula sod is decomposed with the... 

Another method for achieving selective pinacol rearrangement involves synthesis of a glycol monosulfonate ester. These compounds rearrange under the influence of base. 

Acetic acid appears to function both as an accelerator for the oxidation and an inhibitor of the rearrangement to glycolic acid. 

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