Cyclopropylcuprate

The coupling reaction of the cyclopropylcuprates 87 with the 4-chloro-cyclobutenones 75 or their ethylene acetals 86 is useful for preparing the 4-cyclopropyl-2-cyclobutenones 88. The ring fission of 88 to the cyclohep-tadienones 89 is performed by a Rh(I)-catalyst. The less substituted cyclopropane ring bond is cleaved selectively. Cyclooctadienones are obtained by using 4-cyclobutyl-2-cyclobutenones [43]. (Scheme 31)... 

The related lithium(phenylthio)cyclopropylcuprate, prepared from cyclopropyllithium and PhSCu, has been extensively used in the synthesis of /1-cyclopropyl enones by coupling with the corresponding fl-iodo enones (equation 10)34 36. Repetitive regioselective coupling of ethynylcyclopropane units by this method led to polyspirocyclopropyl acetylenes as precursors to [NJpericyclynes37. 

The bicyclo[S.4.0]undecane sesquitetpenoid ( )-3-himachalene (109) was prepared via a route in which thermolysis of a 3-(2-vinylcyclopropyl) enone played a key role (Scheme 15). Reaction of the P-iodo enone (82) with the stereochemically homogeneous cyclopropylcuprate (106) provides the functionalized trans-divinylcyclopropane (107). Thermolysis of (107) gives exclusively the Cope reanange-ment product (108), which is converted into ( )-P-himachalene (1()9). Notably, in contrast to structurally related systems (vide supra), the p, y-unsaturated ketone function in (108) shows no inclination to rearrange to the corresponding a,P-unsaturated (conjugated) ketone. 

When monosubstituted ketals 18 are used, the addition of lithium dialkylcuprates mainly yields the cyclopropylcuprates with a newly created quaternary center, namely 19A, in 90-100 /o selectivity. ... 

The route to cyclopentanes via thermolysis of vinylcyclopropanes is an attractive one, limited only by the availability of the vinylcyclopropane. Trost s use of (32) offers one solution to this problem, but in related investigations Piers et and also Marino and Browne, have demonstrated that the vinylcyclopropanes are smoothly produced by reaction between lithium cyclopropylcuprates (37) and jS-halogeno-ajS-unsaturated ketones, according to Scheme 13. Furthermore, Marino and Browne have found that conjugate addition of (37) to acetylenic ketones offers additional scope for the synthesis of monocyclic vinylcyclopropanes, e.g. (38) (39). 

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