Cyclohexenones carbonylation

OO stretch cyclohexenone carbonyl C—C stretch, aromatic and cyclic unsaturation OC stretch, aromatic C-0 stretch, aryl methoxyl... 

Analysis of the apparently competing factors which cause these differences between cyclic and acyclic systems is incomplete. The effect of substituents on the 17o NMR chemical shifts of simple cyclohexenones (31-33) has been investigated [67]. Both a and P alkyl groups cause shielding of the cyclohexenone carbonyl signal (cf. 32 and 33 with 31). 

The Y appendage of 2-cyclohexenone 191 cannot be directly disconnected by an alkylation transform. (y-Extended enolates derived from 2-cyclohexenones undergo alkylation a- rather than y- to the carbonyl group). However, 191 can be converted to 192 by application of the retro-Michael transform. The synthesis of 192 from methoxybenzene by way of the Birch reduction product 193 is straightforward. Another synthesis of 191 (free acid) is outlined in... 

Display and describe the lowest-unoccupied molecular orbital (LUMO) for cyclohexenone. This is the orbital into which the nucleophile s pair of electrons will go. Does it anticipate both carbonyl and Michael products of nucleophilic addition Explain. A clearer picture is provided by a LUMO map for cyclohexenone. This gives the value of the LUMO on the accessible surface of the molecule, i.e., on the molecule s electron density surface. Does it anticipate both of the observed products If so, which should be the dominant Explain your choice. 

Carbonyl condensation reactions are widely used in synthesis. One example of their versatility is the Robinson anuulation reaction, which leads to the formation of an substituted cyclohexenone. Treatment of a /3-diketone or /3-keto ester with an a,/3-unsaturated ketone leads first to a Michael addition, which is followed by intramolecular aldol cyclization. Condensation reactions are also used widely in nature for the biosynthesis of such molecules as fats and steroids. 

Most investigations of the photocycloaddition of simple a,0-unsaturated carbonyls have involved the reactions of the ring compounds cyclopentenone and cyclohexenone. The photoaddition of 2-cyelohexenone to a number of different olefins has been reported by Corey and co-workers(94) ... 

Carbonyl insertion is preferentially observed in the photoindueed reaction of 22 to give the cyclohexenones 25 and 26 as shown in Scheme 9 [17]. The acyl complex 24 is involved as an intermediate. The eyclohexenone formation appears to be susceptible to conformational effect, as observed in the facile rearrangement of 27 to 28. 

Carbonylative [5 + l]-cycloaddition of allenylcydopropanes was successfully achieved by use of an Ir(I) catalyst to yield (2-alkylidene)cyclohexenones in good yields (Scheme 16.43) [43]. No carbonylative [5 + l]-cycloaddition was observed in the case of an allenylcyclopropane lacking substituents at the allenic terminus. It can be deduced that the metal is too distant to open the cyclopropane ring, probably owing to the preferred -coordination at the allenic Jt-bond distal to the cyclopropyl group. 

The solvent isotope effect produces an A-ratio (HOH/DOD) of three with isotope-independent A// of 17-18 kJ/mol. This result is more difficult to interpret, because it is unknown how many isotopic sites in the enzyme or water structure contribute to the isotope effect of 2-3. If a single site should be the origin of the effect, then the site could reasonably be a solvent-derived protonic site of the enzyme involved in general-acid catalysis of the hydride transfer, most simply by protonic interaction with the carbonyl oxygen of cyclohexenone or possibly by proton transfer to an olefinic carbon of cyclohexenone. 

The intrinsic basicities of cyclopentenone and cyclohexenone (59), and their lactone analogues (60), have been accessed via measurement of their gas-phase proton affinities, and compared with the saturated carbonyl compounds in both cases. The results... 

Murakami and Ito reported a novel iridium-catalyzed carbonylative ring expansion of allenylcyclopropanes [29]. When a mixture of substituted allenylcyclo-propane 49a (R = R = Et, R = R = H) and 5 mol% of IrCl(CO)(PPh3)2 in xylene is heated at 130°C under 5 atm pressure of CO for 35 h, cyclohexenone 53 a is obtained in 81% yield. The reaction is proposed to proceed through in-... 

In the majority of dehydration reactions, heterocyclic compounds are formed, rather than carbocyclic compounds. Many possibilities for formation of carbocyclic compounds exist, but these are important only if (a) the heterocyclic or acyclic tautomers cannot undergo further elimination reactions, or (b) the conditions of reaction greatly favor the formation of an acyclic tautomer capable of affording only the carbocyclic compound. Both five- and six-membered carbocyclic compounds have been isolated, with reductic acid being the compound most frequently reported. Ring closure occurs by an inter-molecular, aldol reaction that involves the carbonyl group and an enolic structure. Many examples of these aldol reactions that lead to formation of carbocyclic rings have been studied.47 As both elimination and addition of a proton are involved, the reaction occurs in both acidic and basic solutions. As examples of the facility of this reaction, pyruvic acid condenses spontaneously to a dibasic acid at room temperature in dilute solution, and such 8-diketones as 29 readily cyclize to form cyclohexenones, presumably by way of 30, either in acid or base. 

In the asymmetric synthesis of 4,4-disubstituted cyclohexenones of the type (132) it was possible to raise the optical yield to a maximum of 54 % by varying the structures of the carbonyl compounds 150) and of the proline derivatives (131)151). 

Cyclic products can be formed by aldol additions provided the donor carbanion and acceptor carbonyl are part of the same molecule. For example, consider how the synthesis of 3-methyl-2-cyclohexenone could be achieved from acyclic substances. The carbon-carbon bond formed in this process of aldol addition closes the ring and ultimately becomes the double bond in the conjugated system when the aldol product undergoes dehydration. Working backwards, we have the sequence... 

---