Ring opening cyclopropanes

The addition of nucleophiles to cyclic fluoroolefins has been reviewed by Park et al. [2 ]. The reaction with alcohols proceeds by addition-elimination to yield the cyclic vinylic ether, as illustrated by tlie reaction of l,2-dichloro-3,3-di-fluorocyclopropene Further reaction results in cyclopropane ring opening at the bond opposite the difluoromethylene carbon to give preferentially the methyl and ortho esters of (Z)-3-chloro-2-fluoroacrylic acid and a small amount of dimethyl malonate [29] (equation 8). 

Karthikeyan S, Q Zhou, Z Zhao, C-L Kao, Z Tao, H Robinson, H-w Liu, H Zhang (2004) Structural analysis of Pseudomonas 1-aminocyclopropane-l-carboxylate deaminase complexes insight into the mechanism of a unique pyridoxal-5 -phosphate dependent cyclopropane ring-opening reaction. Biochemistry 43 13328-13339. 

The threo stereoisomer was the major product obtained by the synthesis in Scheme 13.14. This stereochemistry was established by the conjugate addition in Step A, where a significant (4-6 1) diastereoselectivity was observed. The C(4)-C(7) stereochemical relationship was retained through the remainder of the synthesis. The other special features of this synthesis are in Steps B and C. The mercuric acetate-mediated cyclopropane ring opening was facilitated by the alkoxy substituent.19 The reduction by NaBH4 accomplished both demercuration and reduction of the aldehyde group. 

Cyclopropane ring openings have been proposed to account for the biosynthesis of several unconventional sterols. Ficisterol (106) [70, 71] is of the 26-norergostane type and contains the rare 23-ethyl substituent. Its biosynthesis became apparent following the isolation of the trace cyclopropane sterol,... 

Anyway, the catalysed process is not a clean one, generally also affording five-membered ring 480 and open-chain products 481, as the result of the cyclopropane ring-opening of one or both the methylenecyclopropane addends (Table 37) [116,130,2],... 

The formation of the [5-lactam derivative 597 remains an isolated case. For example, several alkenylidenecyclopropanes react with CSI and toluene-sulfonylisocyanate, but [2 + 2] adducts are formed only by attack on the double bond not linked to the cyclopropane ring when this bond is attacked only products derived from cyclopropane ring opening are formed [158]. 

Internal cyclopropane ring-opening reactions have also been developed using hydroxyl-substituted cyclopropanes. A typical example of this strategy comes from the reaction of the polycylic alcohol 131, which reacts quantitatively with Hg(OAc)2 to yield the acetal 132 (Equation (45)).165 Carbonate moieties can also be used as internal nucleophiles as, for example, in the case of 133, which affords 134 in a 60% yield upon reaction with Hg(OCOCF3) (Equation (46)).166... 

The Tafel rearrangement only occurs in acid medium. Simultaneous reduction of both carbonyl groups leads to interaction and formation of a cyclopropane. Acid catalysed cyclopropane ring opening follows to yield an a-diketone 28 which undergoes the electrochemical Clemmensen reduction step to the hydrocarbon. Side products include the two monoketones derived by partial deoxygenation of the a-diketone and the secondary alcohols from reduction of these raonoketones. Separate experiments show that the a-diketone 28 can be reduced to the hydrocarbon. 

Can Hyperconjugation in a 1,3-Diradical Control the Stereochemistry of Cyclopropane Ring Opening and Make a Singlet the Electronic Ground State of the Diradical ... 

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