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Michael cyclopentanes

The intramolecular Michael addition of acyclic systems is often hampered by competing reactions, i.e., aldol condensations. With the proper choice of Michael donor and acceptor, the intramolecular addition provides a route to tram-substituted cyclopentanones, and cyclopentane and cyclohexane derivatives. Representative examples are the cyclizations of /3-oxo ester substituted enones and a,/J-unsaturated esters. [Pg.968]

Scheldt and co-workers have also accessed enolate equivalents from enals to furnish cyclopentanes 236 asymmetrically. Formation of the enolate equivalent from enals 235 with the NHC, followed by an intramolecular Michael reaction and 0-acylation, gives the lactone products 236, which are readily opened by either alcohols or amines to generate functionalised cyclopentane derivatives 237 in excellent ee. [Pg.289]

Treatment of the diester 211 (E = CC Et) with lithium IV-benzyltrimethylsilylamide, followed by aqueous acid, yields the cyclopentane derivative 212, the product of an intramolecular Michael addition (equation 104)110. 1-Methylindane is produced in moderate yield by the electrochemical reduction of o-bromo-(3-butenyl)benzene (equation 105)111. [Pg.538]

Cathodic reduction of 1,3-diphenyl-propenone leads to l-hydroxy-2-benzoyl-3,4-diphenyl cyclopentanes with exclusive cis configuration of the two phenyl groups. With l-phenyl-l-pentene-3-one the cyclodimer 2-methyl-3,5-diphenyl-4-(l-propionyl)-cyclohexanone is formed with a 100% yield in an intramolecular Michael addition via an electrogenerated base. The substituents are all in the most stable equatorial position [277]. [Pg.430]

Trimethyl aconitate can be cyclodimer-ized in 75% yield and a high stereoselectivity to a pentamethyl l-(2-methoxy-2-oxoethyl)- ,2,3,4,5-cyclopentane pentacar-boxylate. Product formation is initiated by an electrogenerated base that induces a catalytic cycle of two successive Michael additions. The most stable out of 16 possible diastereomers is formed, which indicates that the tandem Michael addition is thermodynamically controlled [282]. [Pg.431]

Other approaches to synthesize highly substituted cyclopentanes, including amino and hydroxy groups, from y- and lactones, has been radical and anionic Michael cyclizations of the a-iodo-y- and -<5-lactones [94]. Likewise, methods using radical cyclization to oxime ethers have been reported to give amino substituted cyclopentanes [95,103,104]. It should be noted that although only one isomer is often obtained [103], such cyclizations generating a secondary radical may not be stereospecific [95,100,101]. [Pg.149]

The synthesis of this compound represents a notable departure from those discussed above. The presence of the carbonyl group at the 9 position of the cyclopentane ring, which classifies this compound as a PGE, removes one asymmetric center and thus somewhat reduces the stereochemical complexity of the synthesis. More importantly, this introduces the possibility of attaching the lower side chain by means of a 1,4-addition reaction the tram relationship of the two side chains should be favored by thermodynamic considerations. The very unusual functionality of the required Michael acceptor, that of a cyclopent-2-en-4-ol-l-one, leads to a rather lengthy albeit straightforward synthesis for the requisite intermediate. [Pg.15]

Intramolecular conjugate allylation (12, 25).2 Fluoride ion catalyzes intramolecular Michael additions of allyltrimethylsilane to a,p-enones as well as a,p-unsaturated esters, nitriles, and amides Lewis acid catalysis is not effective. The method is particularly suited to cyclopentane annelations.2... [Pg.11]

Michael intramolecular alkylation. The reaction of f-butyl lithioacetate (1) with ethyl 6-iodo-2-hexenoate 2 in the presence of potassium t-butoxide in THF at - 78° results in a single trans-1,2-disubstituted cyclopentane (3). Reaction of 2 with f-butyl lithiopropionate (4) under the same conditions results mainly in syn-5, but when HMPT is also present anti-5 is mainly formed. Similar stereoselectivity is observed in reaction of 1 and 4 with ethyl 6-iodo-2-heptenoate in formation of... [Pg.252]

Radical cyclization of p-bromoalkynes.2 Addition of (C6H5)3SnH and AIBN to benzene solutions of a p-bromoalkyne and a Michael acceptor results in annelated cyclopentanes in moderate yield. [Pg.335]

Several groups have prepared cyclopentane systems by intramolecular Michael addition.72 Reaction of the triester (292 Scheme 37) with phenyl vinyl ketone (293) and base produces the cyclopentane (295) in good yield via an intermolecular (giving 294) and subsequent intramolecular Michael addition.72 When the Michael acceptor is a cyclohexenone (Scheme 38), the c/s-fused hydrindanone is produced (298 or 297).72b 72f Spiro systems can also be formed by these reactions (300a,b equation 66) in which the Michael addition gives a spiro ring fusion. [Pg.24]

Marino has reported that the fluoride-induced ring cleavage of l-silyloxy-2-carboalkoxycyclopropanes affords -y-oxo-a-ester enolates, modified homoenolates, which add to Michael acceptors to afford cyclopentanes and cyclopentenes, e.g. (258—>259) 196 alternatively, a carboannulation procedure affords octalin-l-ones (260—>261 Scheme 87) (note the intramolecular enolate addition to the a, -unsaturated sulfone). [Pg.120]

An intramolecular asymmetric Michael addition of aldehydes and ketones - to give cyclopentanals - gives the otherwise disfavoured d.v-producls when catalysed with (f) antibody 38C2, the first commercially available catalytic antibody 222 One case gave 99% de, 98% ee. ... [Pg.25]

Cyclohexan 4-Acetoxy-l-tert.-butyl-4-nitroso- (Isomerenge-misch) IV/ Jb, 260 Cyclopentan 3-Butyl-2-(2-nitro-propyl)-l-oxo- E16d, 231 (Michael-Addition)... [Pg.1069]

Tsuchii et al. reported a very interesting four-component domino process where an alkyne, two olefins and diphenyl diselenide sequentially react to form a highly functionalized cyclopentane derivative, after a linear addition sequence and 5-exo-trig cyclization [136]. This reaction can be seen as an interrupted polymerization process initiated by the addition of selenyl radical to an electron-deficient alkyne in the presence of a large excess of a Michael acceptor. The identity of each reaction partner is important for the outcome of the reaction. For instance, use of (PhS)2 instead of (PhSe)2 leads to the polymerization product rather than to the cyclization one, while (PhTe)2 did... [Pg.31]

The parent (r) -allyl)Fp (3) reacts readily with a highly activated electron-deficient alkene such as dimethyl methylenemdonate at room temperature to give the Fp-cyclopentane (4) (equation 3). As discussed previously, the mechanism apparently involves the initial Michael addition of (3) to the... [Pg.272]

The isolation of cyclopentanecarboxylates from 1,3-diiodopropane and an acrylate in the presence of metallic copper and an alkyl isonitrile has been reported by Saegusa and coworkers (equation 39). The reaction is proposed to involve formation of a transient 3-iodopropylcopper-isonitrile complex (47) from the diiodopropane, which then adds to the unsaturated ester in a Michael fashion (equation 40). The nonconcertedness of this reaction results in stereoselective cycloaddition. For example, Iratfa diethyl ma-leate and fumarate produce the same cyclopentane adduct in identical yields (equation 41). The generality of this cycloaddition has not been explored. [Pg.282]

Winterfeldf s synthesis of brefeldin A (Scheme 1.36) also entailed use of a Michael addition in an anti fashion to a 4-substituted cyclopentenone. Dithiane anion 217 was added in a 1,4 sense to enone 216 to give, after elimination of acetic acid, cyclopentenone 218. Addition of cuprate 219 to 218 in the expected anti manner cleanly afforded the trans cyclopentane 220. Hydride reduction gave the unnatural P-alcohol, which was inverted by a Mitsunobu reaction and the resulting ester cleaved to the desired a-alcohol 221. Protection of the alcohol... [Pg.34]

Michael additions of heteroatoms can be coupled to reactions of the specific enolate produced. The synthesis of the modified carbonucleoside (-)-neoplanocin A 92 required some cyclopentane to which the heterocyclic purine could be joined. The decision was taken to close the cyclopentane by an aldol reaction. This required an aldehyde and an ester in a compound such as 94 to combine regio- and stereo-selectively without epimerisation of any chiral centres. The aldehyde is enolis-able so there are serious problems.33... [Pg.136]

Figure 6.6 shows our synthetic plan for testudinariol A (149). Because the structural feature of target molecule 149 is its C2-symmetry, 149 can be obtained by dimerization or its equivalent operation of A. The intermediate A may be prepared from B by (Z)-selective installation of the two-carbon appendage. For the stereoselective construction of the cyclopentane portion of B, an intramolecular ene reaction is appropriate employing C as the substrate. The intramolecular oxy-Michael-type cyclization of D has been adopted to prepare the tetrahydropyran ring of C. The intermediate D can be synthesized from F [(R)-glycidol] via the known diol E. [Pg.227]

An intramolecular Michael reaction (catalyzed by 2C) following the oxidative dearomatization of 4-substituted phenols provides valuable octalones. A method involving two consecutive Michael reactions to form optically active polysubstituted cyclopentanes should be highly rated. [Pg.377]

The required cyclopentane component was derived (ref. 60) by the sequence of reactions depicted in Scheme 19. The diketo ester shown is available from the cyclisation with sodium ethoxide of the Michael adduct of diethylmethylmalonate with mesityl oxide. The less hindered... [Pg.757]


See other pages where Michael cyclopentanes is mentioned: [Pg.221]    [Pg.140]    [Pg.317]    [Pg.646]    [Pg.231]    [Pg.543]    [Pg.24]    [Pg.742]    [Pg.437]    [Pg.404]    [Pg.80]    [Pg.85]    [Pg.3220]    [Pg.570]    [Pg.609]    [Pg.192]    [Pg.110]    [Pg.556]   
See also in sourсe #XX -- [ Pg.328 , Pg.332 , Pg.353 , Pg.354 , Pg.367 ]




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