Cyclopropanecarboxaldehydes

Bicyclobutane has been prepared by intramolecular addition of a divalent carbon to an olefinic double bond,1 2 irradiation of butadiene,3 decomposition of cyclopropanecarboxaldehyde tosylhydrazone,4 and deamination of cyclobutylamine and cyclopropylcarbinylamine.5 The present procedure is based upon a published method.6 This procedure gives the highest yield of the known methods and provides a process for making moderate quantities of material. 

Electron dilfraction (64TL705) and microwave spectroscopy (65JCP647) of cyclopropanecarboxaldehyde exhibit a twofold barrier for internal rotation, and the two conformers possess almost the same energy content in the gas phase. Ab initio MO calculations (83JST(104)1 IS) in the extended b-BlG basis set predict the s-cis form to be more stable than the s-trans, with the transition state located at 0 a 100°. A twofold barrier was also found (65JCP3043) by electron diffraction for cyclopropyl methyl ketone, with the s-trans isomer destabilized by steric interactions with respect to the aldehyde. 

The major reaction in the thermal decomposition of 2,3-dihydrofuran (9) is a unimolecular isomerization to cyclopropanecarboxaldehyde (89JPC-1139). In an analogous [1,3] sigmatropic reaction, the isomerization of 2-methyl-4,5-dihydrofuran (10) leads to acetylcyclopropane, which can rearrange to 3-penten-2-one (94JPC2341). The latter product may also be formed directly from 10. 

Otherwise, cuprous iodide-catalyzed addition of methylmagnesium iodide to 2-cyclohexen-l-one in ether at 0 °C, followed by trapping of the resultant enolate anion 188 with cyclopropanecarboxaldehyde 189, afforded the two diastereomers of the cyclopropylcarbinol 190 a. Further transformation into the corresponding acetates 190b (acetic anhydride, pyridine), followed by treatment with l,5-diazabicyclo[4.3.0]-non-5-ene (DBN) in refluxing benzene, provided in 78 % yield, a mixture of the desired P-cyclopropyl enones 191 and 192, in a ratio of 13 1, Eq. (60) 127). 

Furthermore, such a C3 -> C4 ring expansion could even be induced by lithium chloride. Thus, the cyclopropylcarbinol 228, prepared by addition of acetylenic Grignard reagents to the cyclopropanecarboxaldehyde 171a in 80-90% yield1101, was transformed into the tosylate 229 upon successive treatment with one equivalent of methyllithium in ether at 0 °C and with one equivalent of tosyl chloride at —40 °C, lithium chloride being formed as by-product. The formation of tosylate 229 appeared, however, to be strongly dependent upon the nature of the solvent effectively, the same... 

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-... 

A solution of bromine (31.5 mmol) dissolved in 20 ml acetonitrile was cooled to — 15°C and hexaethylphosphorous triamide (34.1 mmol) added at such a rate the temperature was kept below 10°C. When the addition was completed sodium azide (34.2 mmol) was added and the resulting suspension allowed to warm to ambient temperature over 2 hours. The mixture was re-cooled to — 15°C and dimethyl-2-oxopropyl phosphate (28.6 mmol) and DBU (0.65 mmol) added. The solids were filtered off after 45 minutes, washed with acetonitrile, cyclopropanecarboxaldehyde (24.5 mmol) dissolved in 200 ml methyl alcohol containing K2CO3 (57.8 mmol) added, and the mixture stirred at ambient temperature 16 hours. The mixture was cooled to 0°C, diluted with 250 ml ice-cold water, and the product extracted 3 times with 30 ml n-octane. The extracts were combined, dried, and the product isolated in 73% yield. 

Pitts et photolyzing cyclopropanecarboxaldehyde at 3130 A in the temperature range 100-200 °C, detected a new product, which was identified by infrared spectroscopy as crotonaldehyde (characteristic absorption at 1140 and 1150 A). The quantum yield of its formation was found to be 0.35 at 120 °C and was only slightly influenced by temperature increase. (Under the same conditions ( CsHe (/>co are 0.25 and 0.30, respectively.) Crotonaldehyde is formed by the isomerization of cyclopropanecarboxaldehyde in the primary process... 

---