Cyclopropane ring alcohols

The hydrogenolyaia of cyclopropane rings (C—C bond cleavage) has been described on p, 105. In syntheses of complex molecules reductive cleavage of alcohols, epoxides, and enol ethers of 5-keto esters are the most important examples, and some selectivity rules will be given. Primary alcohols are converted into tosylates much faster than secondary alcohols. The tosylate group is substituted by hydrogen upon treatment with LiAlH (W. Zorbach, 1961). Epoxides are also easily opened by LiAlH. The hydride ion attacks the less hindered carbon atom of the epoxide (H.B. Henhest, 1956). The reduction of sterically hindered enol ethers of 9-keto esters with lithium in ammonia leads to the a,/S-unsaturated ester and subsequently to the saturated ester in reasonable yields (R.M. Coates, 1970). Tributyltin hydride reduces halides to hydrocarbons stereoselectively in a free-radical chain reaction (L.W. Menapace, 1964) and reacts only slowly with C 0 and C—C double bonds (W.T. Brady, 1970 H.G. Kuivila, 1968). 

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). 

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... 

Figure 8b shows pyrethroid esters composed of an acid moiety without a cyclopropane ring and a phenoxybenzyl alcohol group. While a cyclopropane ring had long been considered an indispensable acid component constituting a pyrethroid skeleton, Ohno et al. [41] in 1974 developed fenvalerate (32), a-isopropylphenyl acetate derivative, with no cyclopropane ring in its acid moiety. This compound exhibits... 

The next step is not immediately obvious. The generation of an ethyl ester from a lactone can be accommodated by transesterification (we might alternatively consider esterification of the free hydroxyacid). The incorporation of chlorine where we effectively had the alcohol part of the lactone leads us to nucleophilic substitution. That it can be SnI is a consequence of the tertiary site. Cyclopropane ring formation from an Sn2 reaction in which an enolate anion displaces a halide should be deducible from the structural relationships and basic conditions. 

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. 

Recent evidence seems to indicate, however, that radical reactions inside a zeolite do not necessarily follow the same pathways as classical radical reactions. The oxidation of the hydrocarbon ethylcyclopropane with H202 catalyzed by TS-1, which should proceed through radical intermediates, gives only the alcohol (27%) and the ketone (73%) resulting from hydrogen abstraction at the carbon linked to the cyclopropane ring, and not the products that would be expected from the rearrangement of the radical intermediate ... 

Cyclopropylcarbinyl radicalsGeneration of a radical adjacent to a cyclopropyl group is attended by cleavage of the cyclopropane ring. The precursors are available by cyclopropanation of a cyclic allylic alcohol followed by replacement of... 

Another interesting transformation of alcohols was effected using bicyclic 1-alkanols with a fused cyclopropane ring, which were cleaved oxidatively to alkenoic acids [131] ... 

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