Bis cyclopropanation

The thermally formed difluorocarbene adds stereospecifically to either (Z)- or ( )-butene to form the corresponding dimethyldifluorocyclopropanes, which points to a singlet difluorocarbene. With butadiene mono- (220) and bis-cyclopropanated product (221) are formed, and with perfluorobutadiene the mono-adduct (222) results 65JA758). 

More recently, the bis-cyclopropanation of dienyne 325 has also been investigated by Fensterbank, Malacria, and Marco-Contelles to construct highly strained cyclopropyl-substituted diquinane frameworks 327 in a completely diastereoselective manner (Scheme 84). 3 It is noteworthy that the formal metathesis product was also observed in these reactions, albeit as a minor product, and that a simple introduction of a methyl group to one of the two ene moieties substantially affects the reaction. 

Scheme 10.17 Tether-controlled regio- and stereoselective preparation of bis(cyclopropanated) Qq derivatives and examples ofbisadducts produced.

Determination of the absolute configurations of these optically active fullerene derivatives was possible by comparison of their experimental and calculated circular dichroism (CD) spectra [96]. Tether controlled bis-cyclopropanation reactions have been extensively used to synthesize extended fimctional architectures such as dyads. 

Figure 7 Enantioselective synthesis of (fA)-22 and (fC)-22 by diastereoselective tether-directed bis-cyclopropanation of C60, followed by transesterification.

Attack by dihalocarbenes on diphenyltropone 522a (Scheme 137) leads to mono- and bis-cyclopropanation [525,526 77BSF(2)571]. With dichloro-carbene, bis(carbethoxy) (522b) and dimethyl derivatives give mono- or bishomotropones, respectively. 

The selective cyclopropanation of the a-enone silyl enol ether 75, by methylene iodide and the zinc-silver couple 2), is remarkable. Only the double bond bearing the tri-methylsiloxy group reacted to yield the 1-trimethylsiloxy vinylcyclopropane 76 when not more than 1.1 equivalent of the Simmons-Smith reagent was used, but the bis-cyclopropanation product 77 was obtained in good yield with an excess (3 equivalents) of the cyclopropanating reagent, Eq. (24) 42). 

The cyclopropanation of (E,E)- and ( ,Z)-bis(styryl) sulfones 7 with sulfonium ylides leads to the formation of tranj-bis-cyclopropanated products 8 only. The stereochemistry of addition of dimethyloxosulfonium methanide to (E,Z)- and ( , )-bis(styryl) sulfones is explained as follows. The addition results in an intermediate which may rotate in such a way that the aryl and sulfonyl groups assume a trans orientation leading finally to the products. 

Reduction of dispiro[bis(cyclopropane)indan]yl methyl oxalate 50 led to the formation of all three possible products derived from the cleavage of one cyclopropane ring. ... 

At this stage an important question may be asked how much of the stability of the bis-cyclopropane oxidized form is associated to its complexation to the copper(I) cluster The isolation of an uncomplexed biscyclopropaneporphyrinogen bonded to an iron(III) ion, complex 15, as reported in reaction (8) clearly answers this question. 

Double cyclopropanation of benzene occurs in the Rh(II)-catalyzed reaction of dimethyl diazomalonate 22. Heating a benzene solution of this diazo compound and rhodium(II) acetate (1 mol %) under reflux gives a mixture of [23 + 24] (19%), 25 (8% yield) and bis-cyclopropanation product 26 (58% yield). When the same reaction is carried out using rhodium(II) trifluoroacetate instead of rhodium(II) acetate as the catalyst, a vastly different product distiibution is obtained [23 + 24], 64% 25, 32% 26, 4%. The low yield of double cyclopropanation product 26 obtained with rhodium(II) trifluoroacetate is comparable to other carbenoid reactions with aromatic substrates, where double cyclopropanation is rare. 

In gold catalyzed transformations, the carbenoid intermediates such as 31 arising from a 5-exo-dig cyclization can also be either oxidized in the presence of Ph2SO leading to carbaldehyde 32 or trapped by an alkene to give bis-cyclopropanic derivatives 33 (Scheme 5.12) [55-57]. 

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