Bicyclic cyclopropanes

Bicyclic cyclopropanes.1 Reaction of the Fisher carbene 1 with the 1,6-enyne 2 results in the bicyclic cyclopropane 3 (a bicyclo[3.1.0]hexane) in 69% yield. The 1,7-enyne homolog of 2 reacts with 1 in the same way to form a bicyclo[4.1.0]-... 

Cationic cyclization. A key step in the synthesis of the diterpenes cafestol5 and atractyligenin4 involves a novel cation cyclization of bicyclic cyclopropanes to the tetracyclic systems of the diterpenes (equations I and II). Thus treatment of 1 with a slight excess of triflic anhydride and 2,6-lutidine effects cyclization to the rather unstable pentacycle 2 with the kaurene system. The related conversion of 3 to 4 can be effected with triflic anhydride and 2,6-di-r-butyl-4-methylpyridine in 1-nitropropane. 

Moszner et al. (5) prepared low shrinkage dental compositions containing bicyclic cyclopropane derivatives, (V). 

Fluorinated dihalocarbenes have been used as central synthons in the synthesis of fluorinated aromatics from cyclopentadienes.62 The reaction proceeds via a fluorinated fused bicyclic cyclopropane, which upon heating undergoes a ring opening to achieve the ring expansion of the second cycle. 

Lastly, silver-assisted removal of halide has been used to facilitate a Favorskii rearrangement in the key step of the synthesis of the natural sesquiterpene ( )-sirenin (equation 190)989. Fused bicyclic cyclopropane derivatives have also been made by a similar... 

Another case of increased strain is found with the trans-fused bicyclic cyclopropanes. With an eight-membered ring, the cis- and trans-fused compounds have essentially the... 

Finally, the rotations of some more bicyclic cyclopropanes shall be considered. The emphasis will be on the effect of the cyclopropane moiety on the rotations of some selected systems. At first, cis- and traws-3,4-methylene-L-proline (94, 95) shall be compared with... 

Oxidative ring-opening with pyridinium chlorochromate (PCC) gives p, y-unsaturated ketones (equation 24). Formation of chlorinated byproducts could be suppressed by employing certain additives (AgNOj, H20). However, bicyclic cyclopropanes afford only moderate yields. 

Coupling of a Fischer carbene complex with an alkene can generate a vinylcarbene intermediate 12 via an insertion-rearrangement reaction, which can then further react with a double bond. For intramolecular reactions of tethered enynes 10, the products formed are bicyclic cyclopropanes 14 intermolecular reactions lead to cycloalkenylcyclopropanes. 

The majority of the bicyclic cyclopropanes so obtained undergo facile acid-catalyzed ring open-ing/isomerization to the corresponding (Z,Z)-6-oxohexa-2,4-dienoates this transformation already occurs when the workup by column chromatography is performed on silica gel rather than on alumina. Treatment of the bicyclic systems (as well as the E,Z- and Z,Z-dienes) with iodine in dichloromethane results in isomerization to (is,is)-l,4-diacylbuta-l,3-dienes in high yield.The ring-opened products in carbenoid reactions of furans are not likely to result from isomerization of the alkyl-2-oxabicyclo[3.1.0]hex-3-ene-e c/o-6-carboxylates. For mechanistic proposals, see refs 300 and 301. 

In the absence of water, the ester function was retained and a oxo carbonyl group was formed at the original alkoxy-substituted tertiary cyclopropane carbon atom, as demonstrated by the ring opening of bicyclic cyclopropane, e.g. 11 ° and 13, and spirocyclopropane, e.g. 

The nitroisoxazole (35) underwent Diels-Alder reaction with 2,3-dimethyl butadiene to form the adduct (36) (Equation (5)) <90JOC1227>. The nitroisoxazole ester (37) with 2-diazopropane yielded the bicyclic cyclopropane (39), via an unstable adduct (38) (Scheme 4) <87cci077>. The same ester... 

Cyclopropanation of methyl (/ )-2-ter/-butyl-2,3-dihydrooxazole-3-carboxylates with the di-iodomethane/diethylzinc reagent furnishes the bicyclic cyclopropane derivatives 15 with excellent diastereoselectivity76. These intermediates should be suitable starting materials for enan-tiomerically pure /l-aminocyclopropanol derivatives,... 

In the two separate, initial reports on the reactivity of Fischer carbenes with enynes, one study found cyclobutanone and furan products [59], while the other found products due to olefin metathesis [60]. These products have turned out to be the exceptions rather than the rule, as enynes have since been found to react with Fischer carbenes to produce bicyclic cyclopropanes quite generally. The proposed mechanistic pathway is included as part of Bq. (28), in which vinylcarbene 10, produced by insertion of the alkyne into the metal carbene, may then cyclize with the pendant olefin to metallacyclobutane 11, leading to product. The first reported version of this reaction suffered from extreme sensitivity to olefin substitution [Eq. (28) compare R=H, Me] often producing side-products due to metathesis (through 11 to yield dienes) and CO insertion (into 10 to yield cyclobutanones and furans) [61]. Since then, several important modifications have been developed which improve yield, provide greater tolerance for alkene substitution, and increase chemoselectivity for the bicyclic cyclopropane... 

Bicyclic cyclopropanes carane and thujane, bicyclic cyclobutane pinane, and bi-cyclo[2.2.1]heptanes such as camphane, isocamphane and fenchane are the most important skeletons of naturally occurring bicyclic monoterpenes... 

Synthesis of N-heterocycles by ring-enlargement reactions through bicyclic cyclopropane intermediates 13KCS886. 

The ring opening of several carbonyl bicyclic cyclopropanes by electron-rich aromatics and SnCl4 has been investigated. The products are highly dependent on the reactants and the method of activating the substrate. 

Fischer carbenes bearing a double bond lead, upon reduction using dihydro-1,4-pyridine, to bicyclic cyclopropanes by intramolecular reaction. The primary alkybdene intermediate complexes formed by reduction (as shown above) are very reactive towards cyclopropanation. - ... 

The Favorski-type reaction of cyclic chloroenamines has provided an elegant entry into bicyclic cyclopropanes, but hitherto the method has not been applied to... 

Sun, H.H., F.J. McEnroe, and W. Fenical Acetoxycrenulide, a New Bicyclic Cyclopropane-Containing Diterpenoid from the Brown Seaweed Dictyota crenulata. 

Chiral cyclopentenone effectively gave bicyclic cyclopropanes in high enantiomeric excesses. Product 23 was a useful precursor for the improved synthesis of C4a and C4(3-methyl analogues of 2-aminobicyclo[3.1.0]hexanes (Scheme 1.18) [31]. Amino acid-derived vinyUcetones... 

Sulfonium ylides were generated by treatment with a cyclic or an acyclic sulfide in the presence of a base. For example, Tang and coworkers generated a sulfonium ylide from corresponding benzylic halide 31 and tetrahydrothiophene 32, and effectively formed bicyclic cyclopropanes... 

Halonium ylides afforded cyclopropanes. Ochiai et al. synthesized halonium ylides and examined cyclopropanation with cyclooctatetraene [60]. Chloronium ylides 61c smoothly underwent progress of cyclopropanation and bicyclic cyclopropane 63 was obtained in 72% yield (Scheme 1.36). 

The treatment of 1,6-enynes with 5mol% amounts of cp RuCl(cod) 382 in the presence of diazoalkanes resulted in the formation of bicyclic cyclopropanes 383 in good yields (Scheme 1.180) [252]. The reaction progressed through the formation of mthenacyclobutene 384, which cleaved to give a mthenium carbene complex 385. A [2-1-2] cycloaddition of the complex 385 with the internal alkene... 

Trost et al. reported the intramolecular cyclopropanation of 1,7-enyne compounds 390 (Scheme 1.182) [256]. A hydroxyl group at the propargyUc position assisted in the complexation of ruthenium. Bicyclic cyclopropane 391 was obtained in good yields. 

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