Cyclopropane ring opening, double bond additions

Cyclopropane rings are opened hydrogenolytically, e.g., over platinum on platinum dioxide (Adam s catalyst) in acetic acid at 2 - 4 bars hydrogen pressure. The bond, which is best accessible to the catalyst and most activated by conjugated substituents, is cleaved selectively (W.J. Irwin, 1968 R.L. Augustine, 1976). Synthetically this reaction is useful as a means to hydromethylate C—C double bonds via carbenoid addition (see p. 74f. Z. Majerski, 1968 C.W. Woodworth, 1968). 

In agreement with the results of experiments on pyrolysis of l,l-bis(trimethyl-silyl)cyclopropane, additional (2/2)CASPT2/6-31G calculations predict that a rapid 1,2-silyl shift will occur in 12a, forming 13a. However, if cis- and trans-l,l-bis(trimethylsilyl)-2,3-dimethylcyclopropanes (11b and 11c) were pyrolyzed, then, as shown in Figure 22.10, the stereochemistry of ring opening could, presumably, still be inferred from the stereochemistry of the double bonds in the expected rearrangement products (13b and 13c). 

Pd-catalyzed C-H transformation at nitriles to methylenecydopropanes 8 affords the terminal 9 and internal alkenes 10, either exclusively or as a mixture of both (Scheme 2, Eq. 4) [9]. The selectivity of product formation depends on the mode of hydropalladation of the carbon-carbon double bond of the methylene-cyclopropane and ring opening. Ring opening normally occurs at the distal bond. Also, the mode of ring opening of methylenecydopropane depends on the chain length of the substituent at the exomethylene carbon. In the addition of malononi-trile lb to 8b, both monoalkylation and dialkylation products are obtained as a 1 1 mixture (Eq. 10). 

An interesting and potentially useful sequence is shown in equation (107). Cyclopropane esters (305) may be prepared by the addition of diazo esters (304) to double bonds under elimination of nitrogen. After saponification the acid is 0-protonated to open the cyclopropane ring, and the resulting carbenium ion (306) is trapped by lactonization. In effect a "y-lactone has been annulated to a double bond in a re-giodefined manner.Examples are given in Scheme 10. A related reaction involves the conversion of the cyclopropane ester (307) into the lactone (308 equation 108). ... 

The mercury derivatives of bicyclic and monocyclic cyclopropanes underwent ready addition across electron-deficient C —C double bonds. This addition reaction was performed with isolation of the mercury intermediate, e.g. 6, giving and often without isolation of the mercury intermediate giving and 9 directly. Depending on the solvent used (MeOH or HOAc) either methoxide or acetate acted as the nucleophile in the ring-opening reaction. 

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