Cyclohexenones trans

The Robinson annulation of ethyl acetoacetate and trans-chalcone proceeded smoothly to give 6-ethoxycarbonyl-3,5-diphenyl-2-cyclohexenone in 48 % yield. The product was separated from the ionic liquid by solvent extraction with toluene. In both these reactions, the ionic liquid [HMIM][PF6] was recycled and reused with no reduction in the product yield. 

This 1,2-asymmetric induction has been attributed to stcric and stcrcoclectronic factors. Similarly, the cuprate additions to 4-alkylcyclopentenones l7 -19, and 4-alkylcyclohexcnones16 b-18 proceeded with very high trans diastereoselection. The copper iodide catalyzed addition of propylmagnesium bromide to 4-methyl-2-cyclohexenone gave a trans/cis ratio of 80 20, whereas the addition to 5-methyl-2-cyclohexenone produced a transjcis ratio of 93 72 3-Silyloxy system 3 gave the trans-adduct 4 on treatment with butylcopper-boron trifluoride reagent20. 

Stable cA-1-phenyl-1-cyclohexene 24 photodimeiizes via Diels Alder cycloaddition to trans adduct 25 (Equation 1.33) [66] and the photoexcitation of dihydrobenzofuran-fused cyclohexenone 26 in net furan gives the trans fused Diels-Alder adduct 27 (Equation 1.34) [67]. 

A series of chiral phosphinous amides bearing pendant oxazoline rings (50, Ri=H,Tr R2=H,Tr, 51, Ri=H,Tr R2=H,Tr and 54, Ri=H,Tr R2=H,Tr in Scheme 41) have been used as ligands in the copper-catalyzed 1,4-addition of diethylzinc to enones. Two model substrates have been investigated, the cyclic 2-cyclohexenone and the acyclic trans-chalcone. The addition products are obtained quantitatively in up to 67% ee [171]. 

A seven-membered ring is formed in the cyclization of 195 (equation 95)105. The homologue 196 affords the fused cyclooctane 197, together with the cis- and trans-decalinones 198 (equation 96)106. Six-, seven- and eight-membered rings are produced in Lewis acid-catalysed reactions of various cyclohexenones with side-chains terminating in allylic trimethylsilyl groups (equations 97 - 99)107. 

Photocycloaddition of allene to cyclohexenone (341) gave the (3,y-enone (342), which reacted with vinyl magnesium bromide to produce the tertiary alcohol (343) in 79% yield. When the compound (343) was treated with KH and 18-crown-6 in THF at room temperature for two hours and quenched with aq. NH4C1, the cyclobutene (344) was obtained. The thermal ring opening of the cyclobutene (344) proceeded in toluene in a sealed-tube at 180 °C for twelve hours to give a readily separable 5 1 mixture of the civ-olefin (345), and the trans-olefin (346) respectively in 95 % yield. Moreover, (345) could be converted to a mixture of (346) and (345) in the ratio of 10 1 by irradiation. The compounds (345) and (346) possess the skeleton of the germacranes (347), (348) and (349) 122). 

When organocuprates are added either to 4-substituted cydopentenones 1, or to 4-substituted or 5-substituted cyclohexenones (4 and 7), the trans addition product is generally obtained with good to excellent levels of diastereoselectivity (Scheme 6.1) [2-4]. The 6-substituted cydohexenone 10, however, predominantly gave the syn addition product [5, 6j. 

Addition of Lewis acids may not only accelerate the reaction rate of a conjugate addition but may also alter the stereochemical outcome of a cuprate addition. Interestingly when the 6-t-butyl-substituted cyclohexenone derivative 17 was exposed to dibutylcuprate, followed by silylation of the resulting enolate, the cis enol ether 18 was obtained (Scheme 6.3) [8]. If, however, the cuprate addition was performed in the presence of chlorotrimethylsilane, the stereochemical outcome of the conjugate addition reaction was reversed to give trans enol ether 19. 

The first asymmetric procedure consists of the addition of R2Zn to a mixture of aldehyde and enone in the presence of the chiral copper catalyst (Scheme 7.14) [38, 52]. For instance, the tandem addition of Me2Zn and propanal to 2-cyclohexenone in the presence of 1.2 mol% chiral catalyst (S, R, R)-1S gave, after oxidation of the alcohol 51, the diketone 52 in 81% yield and with an ee of 97%. The formation of erythro and threo isomers is due to poor stereocontrol in the aldol step. A variety of trans-2,3-disubstituted cyclohexanones are obtained in this regioselective and enantioselective three-component organozinc reagent coupling. 

In an ideal kinetic resolution (common in enzyme-catalyzed processes), one enantiomer of a racemic substrate is converted tvhile the other is unreactive [70]. In such a kinetic resolution of 5-methyl-2-cyclohexenone, even with 1 equivalent of Me2Zn, the reaction should virtually stop after 50% conversion. This near perfect situation is found with ligand 18 (Fig. 7.10) [71]. Kinetic resolutions of 4-methyl-2-cyclohexenone proceed less selectively (s = 10-27), as might be expected from the lower trans selectivity in 1,4-additions to 4-substituted 2-cyclohexenones [69]. 

The above 1,4-additions were performed with s-cis enones. In the case of the reaction with s-trans enone such as cyclohexenone, bis(iodozincio)methane (3) should... 

Aziridinyl ketones can be synthesized from unsaturated carbonyls using a series of other methods. For example, azabicyclo[4.1.0]heptanone 27 was obtained from cyclohexenone 25 in its reaction with TV-bromotoluenesulfona-mide sodium salt 33 [49] (Scheme 1.10). The reaction of chalcone with N-chlorotoluenesulfonamide in the presence of silver nitrite is described in [50]. Trans-Aziridinyl ketone 18 was synthesized by reacting chalcone 22 with N,N-diamino-l,4-diazoniabicyclo[2.2.2.]octane dinitrate 34 and sodium hydride in 2-propanol [30, 51]. Aziridinyl ketones can be obtained in the reaction of a -unsaturated ketones with A,A-dichlorosulfonamines [52] and with amines in the presence of lead tetraacetate and trifluoroacetic acid [53] or in the presence of triethylammonium acetate under electrochemical reaction conditions [54]. 

Photoirradiations of both neat and benzene solution of 2-cyclohexenone (92) give a complex mixture of the syn/trans-93 and anti/trans dimer, and two other dimers... 

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