3- Oxabicyclo hexan-2-ones

Hall and his co-workers43 synthesized several 2-oxabicyclo[2.1.1 ]hexan-3-ones from the corresponding 3-chlorocyclobutanecarboxylic acids. These monomers polymerized readily when heated with a variety of basic or acidic initiators. Some of the results of the polymerization are listed in Table 2. 

In the simplest case, the reaction of allyl diazoacetate, the catalyst (iS )-198 or (f )-198 in a concentration as low as 0.1 mol% can still catalyze the formation of enantiomeric-3-oxabicyclo[3.1.0]hexan-2-ones with 95% ee (Scheme 5-60). Substituted alkyl diazoacetates undergo intramolecular cyclopropanation, with similarly high enantiomeric excess (Scheme 5-61).110... 

S. (2R,5S)-2-tert-Butyl-5-methyI-l-aza-3-oxabicyclo[3.3.0Joctan-4-one. In a 250-mL, round-bottomed flask equipped with a magnetic stirrer, 18.3 mL (0.131 mol) of diisopropylamine (Note 10) is mixed with 120 mL of dry tetrahydrofuran (THF, Note 11) under argon. At -78°C bath temperature, 88.6 mL of a 1.6 M solution of butyllithium (0.142 mol) in hexane is added and the mixture is allowed to warm to room temperature for 20 min. After the mixture is recooled to -78°C, the lithium diisopropylamide (LDA) solution is added over a period of 20 min (Note 12) to a Solution of 20.0 g (0.109 mol) of (2R,5S)-2-tert-butyl-l-aza-3-oxabicyclo[3.3.0]octan-4-one in 600 mL of dry THF in a 1-L, round-bottomed flask, precooled to -78°C. Tetrahydrofuran (20 mL) is used to rinse the 250-mL flask. After keeping the resulting solution at -78°C tor 45 min, 8.8 mL (0.142 mol) of iodomethane (Note 13) is added Over a period of 10 min. The resulting mixture is allowed to warm to 0°C over a period Of 3 hr, and 300 mL of a saturated aqueous solution of ammonium chloride is added. 

R,5S)-(-)-6,6-Dimethyl-3-oxabicyclo[3.1,0]hexan-2-one. Highly tnantioselective Intramolecular Cyclopropanation Catalyzed by Dirhodium(ll) Tetrakis[methyl 2-pyrrolidone-5(R)-carboxylate],... 

Irradiation of 2-(prop-2-enyloxy)- and 2-(but-2-enyloxy)cyclohex-2-enones gives 2-oxabicy-clo[2.1.1]hexane and -[3.1.1]heptane derivatives, respectively,17 while 2-(but-3-enoyIoxy)- (7, n = 1) and 2-(pent-4-enoyloxy)cyclohex-2-enone (7, n = 2) afford the cyclohexanone-annulated 2-oxabicyclo[3.2.0]heptan-3-one (8, n = 1) and -[4.2.0]octan-3-one (8, n = 2) derivatives, respectively.18... 

An interesting formal type of Baeyer Villiger reaction was observed in the photolytic rearrangement of e.xo- and enc/o-7,7-diphenyl-2,3-epoxybicyclo[3.2.0]heptan-6-one which both gave f w7o-5-(2,2-diphenylvinyl)-2-oxabicyclo[2.1.1]hexan-3-one (11).32... 

Other y-lactone containing systems that have been studied include derivatives of 3-oxabicyclo[3.1.0]hexan-2-one173 and 3-(2-hydroxybenzylidene)-4,5-dihydrofuran-2(3//)-one (213), which on irradiation in methanol undergoes a trans-cis photoisomerization followed by a photochemically induced trans esterification to give the coumarin (214).174... 

Gerdil, R., Huiyou, L., and Gerald, B. (1999) Organic reactions in the solid state. Reactions of enclathrated 3,4-epoxycyclopentanone (= 6-oxabicyclo[3.1.0]hexan-3-one) in tri-o-thymotide and absolute configuration of 4-hydroxy- and 4-chlorocyclopent-2-en-l-one, Helv. Chim. Acta., 82, 418-434. 

U1IC 2-acyl-4-oxa-2-azaspiro[4.5]dec-7-en-1 - one l-acyl-3-oxabicyclo[3.1.0]hexan-2-one 1,3-alkadiene 540... 

This is the first detailed procedure for the synthesis of a chiral dirhodium(ll) carboxamide catalyst and its application to intramolecular cyclopropanation. The preparation of the ligand, methyl 2-pyrrolidone-5(R)-carboxylate, is adapted from the procedure of Ackermann, Matthes, and Tamm.2 The method for ligand displacement from dirhodium(ll) tetraacetate is an extension of that reported for the synthesis of dirhodium(ll) tetraacetamide.6 The title compound, (1 R,5S)-(-)-6,6-dimethyl-3-oxabicyclo[3.1.0]hexan-2-one, is a synthetic precursor to (1 R,3S)-(+)-cis-chrysanthemic acid.5... 

Michael P. Doyle, William R. Winchester, Marina N. Protopopova, Amy P. Kazala, and Larry J. Westrum 13 (1 R,5S)-(-)-6,6-DIMETHYL-3-OXABICYCLO[3.10]HEXAN-2-ONE. HIGHLY ENANTIOSELECTIVE INTRAMOLECULAR CYCLO-PROPANATION CATALYZED BY DIRHODIUM(II) TETRAKIS[METHYL 2-PYRROLIDONE-5(R)-CARBOXYLATEl... 

SruuTaBaii. ts applied this photochemical reaction to the unsaturated ketone, S-hexen-2-one, whioh reacted intramolcoularly to form the highly strained bicydic oxetane, l-inethyl-2-oxabicyclo-I2.2.0)hexane (LXXV). This structure was supported by the in ared and spectra of the compound. 

Allyic a-diazopropanoates to l-methyl-3-oxabicyclo[3.1.0]hexan-2-ones ... 

Intramolecular cyclopropanation was observed to give 3-oxabicyclo[3.1,0]hexan-2-ones 2 when allyl malonates 1 were oxidized with stoichiometric quantities of manganese(III) acetate and copper(II) acetate in glacial acetic acid. ... 

Cyclopropylacetates from Cyclopent-2-enone and 2-Oxabicyclo 3.1.0]hexan-3-ones... 

Many cyclopropyl chlorides and bromides have been converted to alkoxycyclopropanes by treatment with a strong base, in most cases potassium rerf-butoxide, in an appropriate organic solvent (Table 13). Under such conditions, hydrogen halide elimination takes place, yielding strained cyclopropene intermediates, which are trapped by nucleophilic attack of the alkoxide. Overall, a simple substitution occurs when a bond is formed between the alkoxide group and the carbon atom to which the halide was attached. This is the case when l-chloro-5-methyl-exo-6-phenyl-3-oxabicyclo[3.1.0]hexan-2-one (1) was reacted with potassium /ert-butoxide l-/er/-butoxy-5-methyl-ent/o-6-phenyl-3-oxabicyclo[3.1.0]hexan-2-one (2) was isolated in 94% yield.If a C-O bond is established at the other olefinic carbon atom, a C H bond is concomitantly formed at the carbon atom, to which the halide was attached. The result is a double substitution which is discussed elsewhere (see Section 5.2.1.3 ). When the substrate contains more than one halogen atom, several elimination reactions usually take place. Thus, treatment of 1 -bromo-2-chloro-2-methylcyclopropane (3) with an excess of potassium /er/-butoxide gave l-ter/-butoxy-2-methylenecyclopropane (4) in 30% yield. 

Oxidation of iodine occurred on reaction of c -2-iodocyclopropanecarboxylic acid (1) with various oxidizing agents. Reaction of 1 with peracetic acid apparently gave the corresponding iodoso derivative which reacted further to give l-hydroxy-l-ioda-2-oxabicyclo[3.1.0]hexan-3-one (3) in fair yield. The same compound was obtained when cw-2-(dichloro-A -iodanyl)cyclo-... 

Cyclopropyl ketones have been converted into alkyl cyclopropanecarboxylates using various oxidizing agents. Peracids, such as peracetic acid, 3-chloroperoxybenzoic acid, and tri-fluoroperacetic acid, have been most frequently utilized, ° but the reaction has also been carried out photochemically. A severe problem can be concomitant formation of cyclopropyl carboxylates exo-4-trideuteriomethylbicyclo[3.1.0]hexan-2-one reacted with 3-chloroperoxybenzoic acid to give a significant amount of exo-5-trideuteriomethyl-2-oxabicyclo[4.1.0]heptan-3-one (12%) in addition to exo-5-trideuterio-methyl-3-oxabicyclo[4.1.0]heptan-2-one (49%). - ... 

On the other hand, treatment of 6,6-diphenyl-3-oxabicyclo[3.1.0]hexane-2,4-dione with phenylmagnesium bromide gave the pseudoacid 4-hydroxy-4,6,6-triphenyl-3-oxabi-cyclo[3.1,0]hexan-2-one in low yield (11 %). Replacing the Grignard reagent with diphenyl-... 

Me) at 180°C led to a 7 1 mixture of 4,4-dimethyl-3-oxabicyclo[3.1.0]hexan-2-one (19) and 4,5,5-trimethylfuran-2(5//)-one (20). ° The formation of product 19 can be rationalized by intramolecular addition of the carboxy group across the exocyclic C — C double bond, whereas furanone 20 is probably the result of an intramolecular trapping of the diradical intermediate of the methylenecyclopropane rearrangement. This assumption was confirmed by pyrolysis of the isomeric add, 2,2-dimethyl-3-methylenecyclopropanecarboxylic acid (18, R = Me R = H), which led to the same products, but in a different ratio (2 7). ... 

In spite of the low reactivity of 1,2-disubstituted and trisubstituted olefins in the intermolecular cyclopropanation, some allyl diazoacetates were easily cyclopropanated to give the corresponding 3-oxabicyclo[3.1.0]hexan-2-one derivatives [44]. The trans isomers gave good results (from 76 to 86% ee),but low enan-tioselectivities were observed for the cis derivatives, Eq. (9). The diazo substrates containing a 2-alkyl substituent did not undergo intramolecular cyclopropanation under a variety of reaction conditions. In these cases, carbene dimers were the only isolated products. 

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