Cyclopropanecarboxaldehyde, preparation

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. 

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... 

Given the previously discussed examples of the [S-(-2] cycloaddition, one can imagine a variety of approaches to the synthesis of molecules like dictamnol. One which has found success is given in Scheme 8. The cycloaddition precursor is prepared in three steps fi om commercially available cyclopropanecarboxaldehyde. Cycloaddition of alcohol 68 proceeds in 69% yield to provide cycloadduct 70. The yield of the cycloaddition is improved to 80% by protecting the alcohol as a TBS ether (69), although the combined yield for cycloaddition and deprotection is 70%. With two additional steps from 70, dictanuiol (71a) was prepared in 10% overall yield, marking the first application of the metal-catalyzed [5+2] cycloaddition in natural product synthesis. 

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