1,1′‐Verknüpfung von Cyclopropan‐Derivaten: die helicale Konformation von Quinquecyclopropanol

Convenient Access to Various 1‐Cyclopropylcyclopropane Derivatives

“…[19] The bicyclopropyl substituent in trans,trans-18 adopts the same synclinal (gauche) conformation as that in 1-cyclopropylcyclopropanecarboxylic acid (Figure 1). This is typical for 1-substituted bicyclopropyl derivatives, [11] whereas bicyclopropyl itself in the crystal assumes an antiperiplanar (s-trans) orientation.…”

“…This access to 10m is far superior to a previously published preparation of 2-(bicyclopropyl-1-yl)-1,3,2-dioxaborinane from bicyclopropylidene. [11] Since the boronate 10m was obtained in higher yield (71 %) than the stannane 10b (61 %) and Suzuki couplings [12] are more popular than Stille couplings, [13,14] the palladium-catalyzed cross coupling of 10m with some aryl halides was tested. Suzuki cross couplings of simple cy- Table 1.…”

“…The interest in the 1-and 2-cyclopropylcyclopropyl substituents is growing, [1,2] and this must have to do with the peculiar electronic properties of cyclopropyl substituents in general [24] and the added steric features of substituted bicyclopropyl units, which have a preferred synclinal (gauche) orientation. [11,25] …”

Three-Membered-Ring-Based Molecular Architectures

“…294,295 Starting from trimethylenephenylboronate 416a (R ) Ph), 2-fold insertion of in situ generated bromolithiocyclopropane by bromine-lithium exchange on dibromocyclopropane 417 with n-butyllithium at -110 °C furnished trimethylene 1′-phenylbicyclopropylboronate 419a (R ) Ph) in 19% overall yield (Scheme 65). 296 Further homologation using the same protocol did not succeed. With the methylboronate 416b, however, two further homologation steps succeeded to give 421b (Scheme 65).…”

“…296 The simultaneous synthesis of 419b, 420b, and 421b could also be accomplished using a one-pot protocol, according to which the reaction mixture was cooled again prior to addition of another batch of dibromocyclopropane and n-butyllithium and was slowly warmed to room temperature, in 15%, 21% and 24% overall yield, respectively. 296 Starting from the cyclopropyl-(416c) or the bicyclopropyl boronate (418c), the quinquecyclopropane 421c could be obtained according to the one-pot protocol in 32% and 22% overall yield, respectively, along with 419c and 420c (Scheme 65). 296 Treatment of the boronic esters with hydrogen peroxide under basic conditions furnished the free hydroxyoligocyclopropanes from these.…”