Syntheses of Cyclopentanones

Another synthetic route via the Beckmann rearrangement, which is promoted by organoaluminum reagent along with alkylation, involves a new stereoselective reduction of the imino group. The starting oxime sulfonate (228) was synthesized from cyclopentanone (226) in three steps Reaction of 226 with 1-undecene in the presence of silver oxide produced the a-undecylcyclopentanone (227) which on successive treatment with hydroxylamine and methanesulfonyl chlo-ride-triethylamine gave the mesylate (228). Treatment of the oxime mesylate... 

A series of 4-heteroaryl-5,6-di(2,5-dimethyl-3-thienyl)-2-phenyM//-l,6-thiazines 54 with photochromic properties was prepared by reacting 3-(2-(2,5-dimethylthiophen-3-yl)ethynyl)-2,5-di ethylthiophene with thiobenzamide and aldehydes <2005CHE86, 2005PS1503>. The acid-catalyzed cyclocondensation of cyclopentanone, aromatic aldehydes, ArCHO, and thiourea affords the cyclopenta[t ]l,3-thiazines 37 <2006PS1655>. Two equivalents of the aldehyde are required. The same products are isolated when 2,5-dibenzylidenecyclopentanones are treated with thiourea under the same conditions. 2-Amino-4i/-l,3-thiazines 184 are easily synthesized in one pot by the reaction of aromatic alkynes, R feCH, aromatic aldehydes, R CHO, and thiourea in the presence of TFA/acetic acid <2005OL3797>. 

Steric control elements are also important for the diastereoselectivity in alkylations of mono-cyclic cyclohexanone enolates. However, electronic control becomes more evident in these systems compared to monocyclic cyclopentanone enolates The flexibility of the six-membered ring system, and the large number of possible ring conformations, makes predictions of the diastereoselectivity difficult. In general, one may conclude that the diastereoselectivity in alkylations of enolates derived from monocyclic cyclohexanones is not as high as in alkylations of cyclopentanone enolates. The syntheses of compounds 21-27 demonstrate the effect of substitution in each position of the six-membered ring49,61 -7°. 

The following application of the synthetic equivalent 110 was carried out. Complex 107 was utilized for the total syntheses of trichothecene (122), trichodiene and trichodermol, applying the reaction of cationic complex 107 with a /f-kcto ester or tin enolate [28]. The tin enolate of cyclopentanone 119 reacted with the complex 107 with high diastereoselectivity to give the diene complex 120 in high yield. After... 

More recently, the formal total syntheses of some bioactive natural products bearing a tetrahydrofurane moiety were achieved by enzymatic Baeyer-Villiger oxidation using cyclopentanone monooxygenases (CPMOs) from Comamonas sp. 

The accessibility to 2,3-disubstituted — and 4,5-disubstituted 2-cyclopentanones by this thermal C3 -< C5 ring expansion has been illustrated by the syntheses of dihydrojasmone 92), cis-Jasmone 92) and dicranenone A188). 

Demethyldeoxynupharidine (5) was synthesized from (—)-castoramine (59) in six steps (Scheme 6) (26). Syntheses of ( )-nupharolutine (50) and of ( )-7-epinupharolutine (60) were completed from cyclopentanone derivative 61 (Scheme 7) (62). A stereocontrolled synthesis of ( )-anhydronupharamine (62) was achieved in six steps from cyclopentanone derivative 63 (Scheme 8) (63). Tufariello (64) pointed out the possibility of synthesizing of 7-demethylodeoxy-nupharidine (5) from nonfunctionalized nitrones such as 64 (Scheme 9). Compound 65, after cyclization and removal of the ketone group, would furnish a synthesis of alkaloid 5. 

However, palladium and nickel catalyzed versions promise, at the moment, an even wider range of possibilities. The need to maintain the catalytic cycle by continuous regeneration of the zerovalent metal catalyst limits, nevertheless, the functionalizability of the metallated center in the cyclized intermediate. For the same reason, the readily accessible starting materials may contain various functional groups which are compatible with the reaction conditions and which may be of value for the syntheses of complex heterocycles such as alkaloids. Carbon monoxide insertion reactions of the cyclized a-metal intermediates were shown to afford monocyclic methyl carboxylates and/or annulated cyclopentanones (cyclopentenones) with concomitant stereocontrolled formation of up to four carbon-carbm bonds. 

Using the approach of the Russian school,the syntheses of 2,4-dimethoxy- and 2,3,4-trimethoxy-oestra-l,3,5(10)-trien-17)S-oU have been developed (Scheme 7). Condensation of 2-methoxy-6-lithionaphthalene (102) with the substituted cyclopentanone (103) afforded the dicarboxylic acid (104). Ring closure gave the tetracyclic derivative (105). Catalytic hydrogenation yielded either the 11-keto-compound (106) or the 11-deoxy-derivative (107), depending on the nature of the catalyst. The 11-keto-compound (106) was subsequently converted into the corresponding oestratriene derivative (108) by reductive processes. 

A particularly useful synthesis of cyclopentanones involves the coupling of an alkene, an alkyne and carbon monoxide in the presence of dicobalt octacarbonyl (equation 17). The reaction proceeds via an al-kyne-cobalt complex (7) and with relatively unreactive alkenes such as cyclopentene it is preferable to synthesize the complex in a separate step. With highly strained alkenes such as norbomadiene, how-... 

Rhodiumcq-catalysed INTRAMOLECULAR ALDER-ENE reaction and syntheses of functionalised a-METHYLENE-y-BUTYROLACTONES AND CYCLOPENTANONES... 

Related synthetic work concerns the preparation of 2-isopropyl-5-methyl-cyclopentanone, syntheses of a number of chiral cyclopentanoid aldehydes and ketones and (113) (c/. Vol. 8, p. 38), and a number of unsuccessful attempts to synthesize genipic acid. ... 

The further route to spiromesifen 8a is similar to the above shown spirodiclo-fen 7f synthesis (Scheme 28.4.3). Acylation of the cyclopentyl hydroxyester 17 (synthesized from cyclopentanone via the classical cyanohydrin route in three steps) with mesitylacetyl chloride 18 leads to the intermediate 19, which is cyclized to the tetronic acid 20 using, e.g., potassium tert-butylate in N,N-dimethylformamide (DMF). 

There has been a good deal of synthetic activity in the methylene-cyclopentanone group of antibiotics during the period under review (c f. 1, 146 2, 97). Two further syntheses of the antitumor agent sarkomycin (81) have been ccmpleted °. Smith has published details of his synthesis of ( )-methylenomycin... 

PROBLEM 18.51 Propose syntheses of the following molecules starting from cyclopentanone ... 

Michael addition of l-lithio-2-methoxycarbonylprop-2-enyl phenyl sulphide to acrylates gives 3-(phenylthio)cyclopentadienones, while addition to aldehydes is followed similarly by cyclization to furan-2-ones. Further uses of vinyl sulphides in syntheses of cyclic compounds include an efficient pentannelation procedure (Scheme 12), cyclization of )i (3-phenylthio-2-methylprop-2-enyl)-)ff-keto-esters to 3-(phenylthio)cyclohexanones, using TFA, and an aromatic substitution reaction [HOCPhjCCSEt)—CHj - 3-phenyl-2-(ethylthio)indene] that involves attack at the yff-carbon atom of the vinyl sulphide moiety, promoted by acid-catalysed dehydration. l-(Phenylthio)vinylphosphonium salts PhSC(=CH PPh3 X , have been advocated for use in the synthesis of cyclopentanone by condensation with... 

Synthesis. Schulse and Winterstein (706, 708) prepared 1 g. of arginine nitrate by allowing a solution of cyanamide and ornithine to evaporate over sulfuric acid for three weeks while Sorensen et al. (747, 750) synthesized arginine nitrate by the reaction of cyanamide and a-benzoylamino-S-amino-n-valeric acid. Ornithine is readily synthesized from cyclopentanone by the methods described by Fox et al. (328) and Albertson and Archer (47) and ornithuric acid ( , -dibenzoylamino-n-valeric acid) is easily prepared by the benzoylation of ornithine. The other steps in the described syntheses of arginine are less satisfactory since they involve either tiie selective reaction of cyanamide with the 8-amino group of ornithine or the selective hydrolysis of the 8-benzoyl group of ornithuric acid. 

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