1.3- Cyclobutanediols

An useful intermediate for the preparation of 1,4-cyclohexanediones is obtained by cycloaddition of 6-isopropyl-3-methyl-2-cyclohexenone to a cyclobutanediol derivative (4.59) 470>. 

Alternative monomers for elimination of crystallinity in PET have been recently proposed. In each of these cases, cyclic monomers were employed, and in most cases, these monomers were alicyclic, and potentially possess sub-7 g molecular motions that could also be of help in dissipating impact energy through molecular motions. The four-membered ring monomer, 2,2,4,4-tetramethyl-l,3-cyclobutanediol (CBDO), first developed by the Shell Chemical Company, has... 

Neopentyl glycol adipate Cyclohexane dimethanol adipate Tetramethyl cyclobutanediol adipate Neopentyl glycol succinate Butane-1,4-diol succinate Phenyl diethanolamine succinate Ethylene glycol sebacate Neopentyl glycol sebacate Ethylene glycol isophthalate Ethylene glycol phthalate... 

B. Cyclopropanecarboxaldehyde. A 50-mL distilling flask equipped with a receiver cooled to -20°C with a dry ice-methanol bath is charged with 34 g (0.39 mol) of a crude mixture of both cis-and trans-1,2-cyclobutanediol and 10 pL of boron trifluoride butyl etherate (Note 8). The mixture is heated to 230°C with a metal bath. Drops of liquid appear on the condenser, and the aldehyde and water distil into the receiver. The temperature of the distillate oscillates between 50°C and 100°C. Each time the distillation stops, 5-10 pL of boron trifluoride butyl etherate is added to the distilling flask (Note 9). The distillate is transferred into a separatory funnel and sodium chloride is added. The organic layer is decanted and the aqueous layer is extracted three times with 25-mL portions of methylene chloride. The combined organic solution is dried over sodium sulfate, and the solvent is removed by distillation through a 15-cm, helix-packed, vacuum-insulated column. The residue con-... 

This method of preparation of the 1,2-cyclobutanedione is an adaptation of that independently described by Denis and Conia3 and by Heine.4 Acyloins, 1,2-cyclobutanediols, imidazole, thioim-idazole, and amino- and cyanofuran derivatives are readily available5, 6 from bis(trimethylsiloxy)alkenes. 

The application of the above principles to simple cyclic structures is straightforward. The fi,Z notation should not be used to define configurations of cyclic compounds such as 1,2-cyclobutanediol. 

R,S)- descriptors can be assigned to prochiral centres in more symmetrical molecules by a simple extension of the sequence rule. For example, in 1,3-cyclobutanediol the OH group at each centre has priority 1 and the H atom priority 4. 

Both CIS- and trans-1,2-cyclobutanediols rearrange under the influence of acid to give the corresponding cyclopropanecarboxaldehydes or ketones in high yields (equation 165) " ... 

In the case of 1-alkylated 1,2-cyclobutanediols, the tertiary hydroxyl is the preferred or exclusive leaving group. With 1,2-dialkylated diols, the trans isomers were normally found to rearrange somewhat more easily than the cis compounds. For instance, trans-1,2-dimethyl-l,2-cyclobutanediol (243) underwent immediate quantitative ring contraction to (1-methylcyclopropyl) methyl ketone (244) upon treatment with boron trifluoride etherate at room temperature while the ring contraction of the cis isomer (245) was observed only on heating at 70°C for 5 min in the presence of BF3 and Et20 (equation 166) . 

The 1,2-cyclobutanediols also undergo thermal rearrangement. The reaction is performed in high yields either in a sealed tube at 230-270°C or in the gas phase. The simple mono- and dialkylated compounds give products which are the same as those formed in the acid-catalysed reaction, and the tram diols were found to rearrange faster than their cis counterparts (equation 166) . 

After the butyl alcohol was removed, the polymers were built up by heating the melt under reduced pressure. Since these polyformals of aliphatic diols had very low melting points (below 75° C.), their utility was limited. Apparently, no higher melting points have been reported for polyformals. In attempts to obtain higher-melting polyformals, the following alicyclic diols were used cis-, trans-, and 1 to 1 cis-/trans- mixture of 2,2,4,4-tetramethyl-l,3-cyclobutanediol (I) trans-1,4-cyclohexanediol (II) tmiw-l,4-cyclohexanedimethanol (III) and 2,5- or 2,6-norbomanediol (IV). 

Materials. 2,2,4,4-Tetramethyl-1,3-cyclobutanediol. The diol was a commercial product (Tennessee Eastman Co.). Unless otherwise indicated, the diol consisted of a cis-/trans- mixture with about a 1 to 1 isomer ratio. The cis-isomer was obtained from the isomer mixture by transforming the trans- isomer into an unsaturated aldehyde with aqueous sulfuric acid (4). The mrw-diol was obtained by preparing the diformate of the isomer mixture, separating the trans-derivative from the cis- derivative by recrystallization, and converting the transdiformate to the diol by methanolysis (5). 

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