1.2- Cyclobutanediol

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. 

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) . 

Likewise, addition of phenylmagnesium bromide in diethyl ether to 2-hydroxycyclobutanone gave m-1-phenyl-1,2-cyclobutanediol (8, 73%), exclusively, which on heating in chloroform containing a catalytic amount of boron trifiuoride-diethyl ether complex, at reflux for two hours, gave 1-phenylcyclopropanecarbaldehyde (9), quantitatively. ... 

Cyclobutanediol, 1,2-dimethyl- synthesis, 53 Cyclobutanone, 2-hydroxy- synthesis, 54 Cyclobutanones synthesis, 77, 79, 335-336 Cyclobutene synthesis, 142... 

Salem, B., Klotz, R, Suffer , J. (2003). Cyclocarbopalladation formation of bicyclic 1,2-cyclobutanediols through a rare 4-exo-dig cyclization. Organic Letters, 5, 845-848. 

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