Cyclopentenes, ozonolysis

In a total synthesis of (+)-brefeldin A, the reagent was elaborated into the a,(3-enone shown, which participated in a palladium-mediated cyclopentene-forming reaction to afford the cxo-olefin. Stereoselectivity in the ring-forming reaction was 3.5 1 in favor of the desired isomer over the alternative trans-cyclopentene. Ozonolysis and reduction of the resulting ketone, followed by protection afforded the MEM ether shown, where all the relevant stereocenters of the final target were established (eq 18). ... 

In order to establish the correct absolute stereochemistry in cyclopentanoid 123 (Scheme 10.11), a chirality transfer strategy was employed with aldehyde 117, obtained from (S)-(-)-limonene (Scheme 10.11). A modified procedure for the conversion of (S)-(-)-limonene to cyclopentene 117 (58 % from limonene) was used [58], and aldehyde 117 was reduced with diisobutylaluminium hydride (DIBAL) (quant.) and alkylated to provide tributylstannane ether 118. This compound underwent a Still-Wittig rearrangement upon treatment with n-butyl lithium (n-BuLi) to yield 119 (75 %, two steps) [59]. The extent to which the chirality transfer was successful was deemed quantitative on the basis of conversion of alcohol 119 to its (+)-(9-methyI mande I ic acid ester and subsequent analysis of optical purity. The ozonolysis (70 %) of 119, protection of the free alcohol as the silyl ether (85 %), and reduction of the ketone with DIBAL (quant.) gave alcohol 120. Elimination of the alcohol in 120 with phosphorus oxychloride-pyridine... 

Oxidation of Ozonolysis Products from 1-Octene and 1-Methyl-cyclopentene. Uncatalyzed autoxidation was performed in a small vessel... 

Interesting variations in product distributions could be observed when ozonolysis was carried out with alkenes adsorbed on silica gel.628 The low-temperature ozonolysis on dry silica gel of cyclopentene led to the formation of the normal, monomeric ozonide in high yield [Eq. (9.114)]. This corresponds to the product formed in aprotic and nonparticipating solvents. In contrast, reaction of cyclopentene on wet silica gel resulted in the formation of the corresponding oxo acid... 

Ozonolysis of silyl ethers of l-cyclopenten-3-ol gives a high selectivity in favor of the exo-substituted ozonide48. The bulkier silyl blocking groups, as shown in entry 37 of Table 1, exhibit a somewhat higher degree of stereo selection. Furthermore, the size of the... 

The monocyclic saturated peroxides 196 have been prepared by the treatment of the respective hydroperoxides with lead tetraacetate (Scheme 94) <1981S633>. Another general approach to the 1,2-dioxepan ring system involves the ozonolysis of appropriate precursors with a double bond e.g., the ozonolysis of cyclopentene gives 1,2-dioxepan (trioxane) 197 . 

Problem 9,20 Predict the ozonolysis products of (a) cydohexene (b) 1-methyl-cyclopentene (c) 3-nieth>lcycloi entenc (d) 1,3-cyclohexadiene (e) 1,4-cyclohexa-diene. 

Diketones are accessible via a number routes, for example by Michael addition of enolate to enone (or precursor Mannich base " ) or by ozonolysis of a cyclopentene precursor. They react with ammonia, with loss of two mole equivalents of water to produce cychc bis-enamines, i.e. 1,4-dihydro-pyridines, which are generally unstable, but can be easily and efficiently dehydrogenated to the aromatic heterocycle. 

The fact that the resultant methylenecyclopentanc can be readily manipulated into the unsubstituted cyclopentene present in the target, highlights the synthetic versatility of the methylene functionality in the cycloaddition products. Alternative manipulations would be conversion to ketone by ozonolysis or to an alkyl-substituted system. 

Parallel studies directed toward luzopeptin E2 focused on the synthesis of A-piz (Scheme 16). Accordingly, Schreiber ozonolysis of cyclopentene furnished 75, which was elaborated to Evans oxazolidinone... 

Ozonolysis of Cyclopentene (A) or Cyclohexene (B) to yield target-drug-molecules hav-... 

Cyclopentene (A) upon ozonolysis undergoes cleavage to give rise to an open-chain compound having carbonyl moieties at C-1 and C-5 positions whereas, cyclohexene (B) 3delds a cleaved product that bears the carbonyl functions at C-1 and C-6 respectively. 

The core skeleton of geissoschizine, an important biosynthetic precursor to numerous polycyclic indole scaffolds, was the target of a nickel-catalyzed alkylative coupling strategy. Cyclization precursor 13 was prepared by ozonolysis and double reductive amination of cyclopentene 12 (Scheme 8.13) [35]. Nickeldeprotection/oxidation sequence followed, and chromatography led to complete inversion of the C3 stereocenter. A Fisher indole synthesis followed to afford ( )-deformyl-isogeissoschizine, the core skeleton of geissoschizine. 

Taber (2002) plan for (-)-codeine oxidative cleavage of cyclopentene ring by ozonolysis followed by recyclization to form cyclohexone ring (steps 16 and 17). 

Ozonolysis of a tetrasuhstituted alkene such as 1,2-dimethylcyclopentene is faster than ozonolysis of a disubstituted alkene such as cyclopentene. Offer an explanation. 

Ozonolysis of the chiral cyclopentene 34 (prepared in several steps from cyclopentadiene), followed by reductive amination and hydrogenolysis affords 1,3-dideoxynojirimycin 35 ... 

Cyclopentene oxide reacted with allylmagnesium bromide and subsequent protection of the resultant alcohol gave 7.262.94 Ozonolysis, Wittig olefmadon,95... 

The opening of the cyclopentene moiety involved the ozonolysis of the double bond and this has been used by Hon for the synthesis of alkenyl butyrolactones. This cyclopentene cycle could also be used for the palladium-catalyzed nucleophilic substitution of the C-4 of the fused lactones. By this strategy, Aggarwal described an access to carbocyclic uracil polyoxin C and the nikkomycins analogues." " ... 

Criegee et al. have examinedthe intramolecular choices of the intermediate carbonyl oxides in the ozonolysis of substituted cyclopentenes (78). Formation of... 

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