Cyclopropanes oxidative cleavage

Scheme 14.21. Formation of cyclopropanes by the oxidative cleavage of titanacyclobutanes. A Me xMe A Me qvie...

Cyelobutanone has been prepared by (1) reaction of diazomethane with ketene,4 (2) treatment of methylenecyclobutane with performic acid, followed by cleavage of the resulting glycol with lead tetraacetate,s (3) ozonolysis of methylenecyclobutane, (4) epoxidation of methylene-cyclopropane followed by acid-catalyzed ring expansion,7 and (5) oxidative cleavage of cyclobutane trimethylene thioketal, which in turn is prepared from 2-(co-chloropropyl)-l,3-dithiane.8... 

Ikegami s successful synthesis of racemic 720 materialized by initial conversion of 701 to 725 via a 1,2-carbonyl transposition sequence (Scheme LXXVIII) Treatment of 725 with methoxycarbene, deprotection, and oxidation provided 72 6. Acid-promoted cyclopropane ring cleavage and added functional group manipulation led to 727 which could be allylated stereoselectively. The tricyclic enone 724 was subsequently produced conventionally. 

Oxidative cleavage of cyclopropanes has been studied mostly with lead(IV), thaIlium(III) and chromium(Vl) reagents. - The oxidative cleavage of cyclobutanols has been explored mainly with chro mium(VI) reagents, although other oxidants have been studied. ... 

As was noted in Scheme 12, distonic radical cations obtained from cyclopropane bond cleavages add oxygen rapidly, producing products with two CO bonds. So do some alkene radical cations. Addition of O2 to an alkene radical cation is formally a nucleophilic attack by the single alkene n electron on O2, and oxidizes both carbon atoms (an alkene radical cations has formally two -f carbons, and the adduct a 1+ and an oxygen-bound carbon). The oxygenation of the radical cation of bia-damantylidine (96) leads to dioxetanes such as 98 in chain reactions (see Scheme 21) [110]. The reactions may be initiated electrochemically or photochemically, but tris(o,p-dibromophenyl)amine hexafluoroantimonate, 97, is a superior catalyst for the dark reaction of certain tetraalkylalkenes, with turnovers up to ca. 800 at... 

When the donor character of the amino substituent at the transition-metal-carbene carbon atom is reduced, it should be possible to influence the thermal stability and reactivity in favor of the desired cyclopropanation process. Indeed, pyrrol-1 -ylcarbene complexes 18 of chromium, molybdenum and tungsten do exhibit the desired reactivity. In the last step, the pyrrole ring of 19 can be converted to the NH2 function in 20 after oxidative cleavage with ozone.In this respect, the pyrrole heterocycle represents a synthetic equivalent of the amino function. 

In a stereochemical investigation of oxidative release of cyclopropanes 12 and 13 from stereochemically defined titanacyclobutanes 9, a straightforward reductive elimination process is discarded in favor of a two-step process. Oxidative cleavage of one metal-carbon bond in 9 with retention of configuration to give 10 and 11 followed by an intramolecular substitution step with inversion at the other carbon forms the cyclopropanes 12 and 13. ... 

Oxidative cleavage of the l,2-bis(siloxy)cyclopropane 8 with aqueous sodium periodate similarly affords 1,3-dione 9, in this case in 37% yield.Upon treatment with iron(III) chloride, 1 -(methylsulfanyl)cyclopropanol undergoes a similar chlorination with ring opening to give a / -chlorinated thioester. ... 

Cyclopropane bonds are susceptible to oxidative cleavage (see Section 2.1.1.2.). Most of the oxidation reactions of activated cyclopropanes involve phenyl-substituted derivatives. When phenylcyclopropane was treated with lead(IV) acetate, 1,3-diacetoxy-l-phenylpropane (63%) and the elimination product cinnamyl acetate (32%) were obtained. The occurrence of traces of l,3-diacetoxy-2-phenylpropane could not be confirmed in later studies. The kinetics of the oxidation of various arylcyclopropanes with lead(IV) acetate, thallium(III) acetate and mercury(II) acetate have been studied. 4-Methoxyphenyl, 4-tolyl, and 4-chlorophenyl derivatives and their meta analogs were treated with these reagents and the rates of reaction and product distributions analyzed. Using lead(IV) acetate, diacetates 1 and cinnamyl acetates 2 were obtained in ratios of about 4 1, whereas thalhum(III) acetate gave the diacetates almost exclusively (see following table). ... 

Car-3-ene is known to be a convenient starting material for access to the irregular chrysanthemyl skeleton (see Section 14). The (+)-olefin has been again stereo-specifically converted (via hydration and oxidation) into (+)-dihydrochrysanthemo-lactone and (+)-methyl m-chrysanthemate.667 668 Other 1,2-cis-cyclopropane derivatives have resulted from oxidative cleavage of derivatives of the same substrate.669-671... 

The acyloin condensation of a,o>-diesters in the presence of MeaSiCl represents a highly efficient method for the synthesis of large rings. The application of the convenient sequence of cyclopropanation/oxidative ring cleavage for ring expansion cf. Eq. (52) to the appropriate m a ocyclic enediol silyl ether 39 provided, a short, high-yield (23% overall) synthesis of muscone ([Pg.37]

Acetals from a,/3-unsaturated aldehydes and optically active 1-aryl-1,3-propanediols are cyclopropanated by the diiodomethane/diethylzinc reagent with moderate selectivity69. After oxidative cleavage of the auxiliary, cyclopropanecarboxylic acids are obtained with 21 -78% ee. Thus, the C2-symmetric auxiliaries seem to be superior for this kind of [2 + 1] cycloaddition. 

Cyclopropanation of the cinnamate 52 followed by oximinatlon gave rac-53. Asymmetric reduction of the oxime ether gave two diastereomers, one of which was taken on to 54 by oxidative cleavage of the furyl group. 

New fragmentation and elimination processes are being developed, leading to milder reaction conditions for olefin formation. A novel fragmentation of l-trimethylsilyloxybicyclo(fi,l,0]alkanes (13) with lead tetra-acetate affords the terminal olehnic acids (14) by oxidative cleavage of both cyclopropane bonds a ... 

Similar concepts are being proposed by Ouelette 123c) to explain oxidative cleavages of cyclopropanes by lead or thallium salts. This is an example of the broad scope of the oxymetallation reaction, as well as its counterpart, the deoxymetallation process. 

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