Cyclopen tenones

An interesting consequence of the base-catalyzed isomerization of unsatu-rated ketones described in Problem 22.37 is that 2-substituted 2-cyclopen tenones can be interconverted with 5-sub tituted 2-cyclopentenones. Propose a mechanism for this isomerization. 

Addition of racemic allylic sulfoxide anions to 2(5//)-furanone gives y-1,4-addition adducts1. The simple and induced diastereoselectivities are completely analogous to that of 2-cyclopen-tenone described earlier. 

The titanium(IV) chloride catalyzed addition of silylenol ethers to 2-substituted cyclopen-tenones stereoselectively yields tnmv-cyclopcntanoncs45 4h. 

A similar trend was observed in the reaction of tri- and tetrasubstituted etiolates derived from 2-unsubstituted or 2-bromo substituted 3,4-dihydro-6-methoxy-1(2//)-naphthalenone16. The trisubstituted cnolate underwent addition to (—)-(2 )-2-(4-methylphenylsulfinyl)-2-cyclopen-tenone via attack on the nonchelated conformation to give an adduct of d.r. [(2S)/(2/ )] 77 23. The tetrasubstituted enolate underwent addition to the corresponding ( + )-(5)-enone via attack on the chelated conformation to give an adduct with the same absolute configuration at C-2 but with d.r. [(2R) (2S)] 95.5-97 4.5-3. 

This type of asymmetric conjugate addition of allylic sulfinyl carbanions to cyclopen-tenones has been applied successfully to total synthesis of some natural products. For example, enantiomerically pure (+ )-hirsutene (29) is prepared (via 28) using as a key step conjugate addition of an allylic sulfinyl carbanion to 2-methyl-2-cyclopentenone (equation 28)65, and (+ )-pentalene (31) is prepared using as a key step kinetically controlled conjugate addition of racemic crotyl sulfinyl carbanion to enantiomerically pure cyclopentenone 30 (equation 29) this kinetic resolution of the crotyl sulfoxide is followed by several chemical transformations leading to (+ )-pentalene (31)68. 

The reaction of 1,3-diamino-1,3-dienes with aryl or a,/J-disubstituted alkenylcarbene complexes leads to the formation of formal [4S+1C] cyclopen-tenones [25a] (Scheme 35). In the case of alkenylcarbene complexes, the substitution of the double bond of the complex in both a- and /J-carbons seems to play a fundamental role as reactions performed in the same conditions but using alkenylcarbene complexes with other substitution patterns leads to compounds of a different nature ([4+3], [4+2] and [2+1] cycloadducts). 

As described previously, the Co-mediated carbonylahve Co-cydization of an alkyne and an alkene, is a very powerful procedure in the preparation of cyclopen-tenones [268], However, depending on the reaction conditions it also allows the preparation of 1,3-dienes, which may be intercepted by a Diels-Alder reaction, as described by Carretero and coworkers [285]. As expected, reaction of 6/4-28 with Co2(CO)8 in refluxing acetonitrile led exclusively to the diastereomeric cyclopen-tenones 6/4-29 and 6/4-30 as a 59 41 mixture. However, using trimethylamine-N-... 

A very new example for the combination of an Au -catalyzed [3,3]-rearrangement and a Nazarov reaction has been disclosed by Zhang and coworker. Thus, cyclopen-tenones could be easily achieved by converting en-ynyl acetates in the presence of AuCl(PPh3)/AgSbF6 [320]. 

The Pauson-Khand reaction (PKR) [96] consists of the synthesis of cyclopen-tenones by reaction of an alkene with a dicobalthexacarbonyl complexed alkyne (Scheme 57) and has recently emerged as one of the methods of choice for the obtainment of five-membered carbocyclic rings [97]. Its unique atom connectivity, which involves the two unsaturated carbons of the reagents and the carbon atom of a carbon monoxide ligand of cobalt usually in a regioselective manner (Scheme 57), has brought to refer to PKR as a [2 -I- 2 + 1] cycloaddition. 

Vinylallenes can also be cydized oxidatively. Vinylallene 61 when treated with vanadyl acetonacetonate and tert-butyl hydroperoxide in benzene produced cyclopen-tenone 63, the immediate precursor of methylenomytin B (cf. 5, Eq. 13.1), in 50%... 

Co2(CO)6 fragments at the C=C triple bonds further from the Pt center. The Pauson-Khand reaction between tra 5-Pt C=CC2H[Co2(CO)6] (PR3)2 (R = Et, Bu) (197) and norbomene or cyclopentene gives the corresponding cyclopen-tenones 198 (Scheme 44). ... 

This strategy culminated in the synthesis of the racemic tricycle 282 as a pair of diastereomers that were separated by chromatography. The cyclopen-tenone 274 served as A-ring building block and the C-ring was synthesized utilizing a Diels-Alder reaction between 279 and 280 as the key step. 

Keywords Alkynylcyclopropanes, Propadienylcyclopropanes, Octacarbonyldicobalt, Cyclopen-tenones, Hydroquinones... 

A formal 13+2 -cycloaddi lion can be accomplished by adding bis(2-carbethoxyethyl) zinc to acetylenic esters . This reaction allows the construction of complex cyclopen-tenones, such as 388, which is a precursor of ( )-bilobalide (Scheme 101) . The allylzincation of tiimethylsilylacetylenes can be performed intramolecularly providing a functionalized alkenylzinc which cyclizes in the presence of Pd(PPh3)4 at 25 "C within 3.5 h, leading to the bicyclic product 389 in 84% yield (Scheme 102). The addition of allylic zinc halides to various alkynes occurs in the absence of copper salts. The related... 

The furan nucleus has also been employed as a building block in the construction of steroid intermediates (73JCS(P1)2420). 2, 4 -Dimethoxyacetophenone was condensed with furfural to give the furfurylidene product (64) which on acid hydrolysis furnished the heptanoic acid (65). Cyclization of (65) proceeded smoothly in alkali to yield the cyclopen-tenone acid (66) which was converted to the cyclopentanaphthalene (67) on boiling in acetic anhydride (Scheme 16). 

M. R. V. Etheridge, Z. C. Khan, S. Hitchcock, P. B. Pairaudeau, G. Vile, S. Stereoselective synthesis of polyfunctionalised hydroxylated cyclopentanes from dihydroxylated 2-cyclopen-tenone derivatives. Tetrahedron 2001, 57, 6295-6303. 

Alkyne-alkene carbonylative coupling. Intramolecular carbonylative coupling of dialkynes catalyzed by Fe(CO)3 provides a route to cyclopentadienones (equation I). The more difficult carbonylative alkyne-alkene coupling to provide cyclopen-tenones (Pauson-Khand reaction) can also be effected with Fe(CO)s, but in modest yield. In an improved coupling, acetone is treated with Fe2(CO)9 to form Fe-... 

C, no esters and furanones are found, but thiazoles, cyclopen-tenones and other heterocyclic compounds dominate. These data imply that esters and furanones are stable at mild temperatures while the formation of thiazoles, cyclopentenones and other heterocyclic compounds require a higher temperature. Also at 160°C, trithiolanes, thiophenones and 2,4-hexanedione predominate, indicating that formation of such compounds is favored by a medium temperature. Bread, crusty and caramel aromas were found in the 100°C sample, pot-roasted, roasted, meaty and clean aromas were found at 160°C, and roasted, roasted-meat, chemical and off-notes were produced at 200°C. 

The photocycloaddition of 1-alkenylboranes in cyclohexane provided m-fused head-to-head adducts for 2-cyclopen-tenone and a mixture of cis- and trans-isomer for 2-cyclohexenone (Equation (71)).397... 

Recently, Toru s group reported on the radical P-addition to the 4- and 5-methyl-2-[(2,4,6-triisopropylphenyl)sulfinyl]-2-cyclopentenone.150The starting cyclopen-tenones 117 and 118 were synthesized by condensation of the vinyl lithium 113 and 114 with DAG 2,4,6-triisopropylbenzenesulfinate 106 to afford 115 and 116, respectively, as a 1 1 diastereomeric mixture in 93% yield. Removal of the acetal group by treatment with acidic silica gel gave the desired cyclopentenones 117 and 118 in 99% yield. 

With the exception of propynoic acid derivatives, all alkynes undergo the reaction. On the other hand, generally, only strained olefins react efficiently in the intermolecular PKR whereas electron deficient alkenes give the reaction only in limited examples. With respect to regioselectivity, the bulkier substituent of the alkyne is placed adjacent to the carbonyl in the cyclopen-tenone product. Unsymmetrical olefins usually give mixtures of regioisomers... 

Finally, a Nicholas-type reaction is presumably responsible for an unexpected result reported by Alcaide. During their work devoted to the application of the PKR in the field of -lactams and azetidines they reacted complexed azetidine 91 with TMANO, isolating a mixture of the expected PK product 92 and by-product 93. The formation of 93 is believed to be a consequence of the ionization of the propargylic C - N bond at the cobalt-acycle step. The crowded metallacycle formed after the insertion of the olefin (93), would prompt the cleavage of the C - N bond, forming an ionic species (94) that would trap a hydride, possibly from a cobalt hydride giving 95, which then would follow the usual pathway towards the cyclopen-tenone (Scheme 27) [124],... 

The cyclobutane derivative 1 is converted under the same conditions to the cyclopen-tenone 2. 

Seven-membered rings can be fused onto the cyclopen-tenone using heteroaromatic enyne-starting materials. A high stereoselectivity is observed in some cases (Scheme 264). 

Kirmse and Streu have used the photocycloaddition of ethene to cyclopen-tenone and 3-methylcyclopentenone to yield the [2 + 2] adducts (32, R = H or Me) as a route to the synthesis of the norbornenones (33). Cyano Dewar heptalene (34) has been successfuUy synthesized using a multi-stage reaction in which the photocycloaddition of ethyne to the enone (35), yielding (36), played an important part. The Dewar heptalene (34) is photochemically labile and is converted into (37) on irradiation with 254 nm light, although it is... 

Lithium /i-butylborohydride is prepared by reacting equimolar amounts of n-butyl lithium and bo-rane dimethyl sulfide complex.This reagent effectively reduces enones in toluene-hexane mixtures at -78 °C to give, in most cases, high yields of the corresponding allylic alcohols.Conjugated cyclopen-tenones, however, give mixtures of 1,2- and 1,4-reduction products. Under identical reaction conditions, saturated ketones are reduced to alcohols. The latter process can take place in the presence of simple esters. 

The pyrolysis of 3-cyclopropyl-3-oxopropanoates (223) at 500-600° C gives 2-cyclopen-tenones in 50-80% yields and cyclopropyl ketones (equation 147). ... 

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