Hetero Cyclic Ketones

In this transformation two new C-C-rr-bonds are formed from three different components. The enantioselectivity of this reaction is generally low (< 5%). With cyclic ketones the corresponding products were obtained as single diastereomers. It is proposed that this reaction involves a Knoevenagel-hetero-Diels-Alder sequence where proline utilizes both iminium and enamine catalysis (Scheme 9.20). 

Effect of Phospholipids on Reaction Volatiles. As would be expected, the inclusion of phospholipids in the reaction mixtures produced many volatiles derived from lipid degradation these included hydrocarbons, alkylfurans, saturated and unsaturated alcohols, aldehydes and ketones. However, two other important observations were made. First, the concentrations of most of the hetero- cyclics, formed by the amino acid + ribose Maillard reaction, were reduced. For most of the major volatiles this reduction was of the order of 40 - 50%, but in the case of thiophenethiol and methyl- furanthiol the reduction was over 65%. This appears to support the findings that in meat and coconut, lipids exert a quenching effect on the amount of heterocyclic compounds formed in Maillard reactions during heat treatment (11,12). Second, and perhaps more important, the addition of phospholipid to the reaction mixtures resulted in the production of large amounts of compounds derived from the interaction of the lipid or its degradation products with Maillard reaction intermediates. 

Therefore, based on the known cyclocondensation of arylidenemalonodinitriles and 1-arylethylidenemalonodinitriles in the presence of piperidine to give 1,6-di-cyanoanilines [66a], Wang and coworkers [67] have developed a straightforward microwave irradiation-assisted pseudo-four-component synthesis of the anilines 62. Thus, the reaction of (hetero)aromatic aldehydes 63, acyclic and cyclic ketones 64 and 2 equiv. of malononitrile in the presence of triethylamine or piperidine furnishes, after 2 min of 300 W-irradiation power, 51-63% of 2,6-dicyanoanilines 62 (Scheme 5.12). 

When phenyl glycine ortho-caxhoxyMc acid is fused with potassium hydroxide it first loses water yielding an acid, indoi llic acid, and this loses carbon dioxide yielding indoxyl. In indoxyl the hydroxyl group is in the 3-position while in the isomeric oxindole it is in the 2-position. All of these comp>ounds are thus condensed hetero-cyclic compounds of a benzene ring and a pyrrole ring. Indole is the mother substance and the others are hydroxy or ketone derivatives. 

Synthesis of cyclic ketones. The reagent has been used in a general synthesis oi cyclic ketones. For example, indene is converted in THF into the Grignard reagent (1) and this is added to 2,3-dichloropropene also in THF. The product (2) is cyclizec to (4) by treatment with 97% formic acid. The method has been extended to hetero-substituted cyclohexanones.2... 

Topics reviewed during the year include the photochemistry of indoles, sulfoxides, pyrazoles and isothiazoles, (S-hetero)cyclic unsaturated carbonyl compounds, photoinduced single electron transfer (SET) reactions of amines and of azo compounds, SET reactions of organosilanes and organostannanes with Qo and ketones, photochromic polypeptides and di(hetero)arylethenes, processes in chromophore sequences on a-helical polypeptides,aryl-aryl coupling in furans, thiophenes and pyrroles," [3+2]cycloaddition of aromatic nitriles (and esters) with alkenes, and reactions of benzylsilane derivatives. ... 

Table 47 Rate and equilibrium constants for ketonization of hydroxy-hetero-cyclic compounds at 25 °C.

Rings s. a. Adamantanes, Alcohols, cyclic, Hetero-cyclics, Isocyclics, Ketones, cyclic, Macrocyclics, Poly-cyclics, Propellanes -, condensed highly condensed s. Cage compds. 

Enamine/metal Lewis acid bifunctional catalysis has been used to achieve good yields, des, and excellent ees in hetero-Diels-Alder reactions of six-membered cyclic ketones ... 

The first highly enantio-selective a-fluorination of ketones using organocatalysis has been accomplished. " The optimal catalytic system, a primary amine-functionalized cinchona alkaloid (24), allows the direct and asymmetric a-fluorination of a variety of carbo- and hetero-cyclic substrates. Furthermore, this protocol also provides diastereo-, regio-, and chemo-selective catalyst control in fluorinations involving complex carbonyl systems (up to 98 2 dr, 99% ee, and >99 1 regiocontrol). 

The nickel-iminophosphine-catalysed 4- -2-cycloaddition of enones with allenes formed highly substituted dihydropyrans. The enantioselective amine-catalysed 4-I-2-cycloaddition of allenoates with oxo-dienes produced polysubstituted dihydropyrans in high yields and with high enantioselectivities. Novel enam-ine/metal Lewis acid bifunctional catalysis has been used in the asymmetric inverse-electron-demand hetero-Diels—Alder reactions of cyclic ketones with Q ,j9-unsaturated a-ketoesters. The 4- -2-cycloaddition of acylketenes (80) with 2-unsubstituted and 2-monosubstituted 3-aryl-2//-azirines (81) produced 1 1 (82) or 2 1 (83) adducts, being derivatives of 5-oxa-l-azabicyclo[4.1.0]hept-3-ene or 5,7-dioxa-l-azabicyclo[4.4.1]undeca-3,8-diene. The formation of the monoadducts proceeds via a stepwise non-pericyclic mechanism (Scheme 25). A-heterocyclic carbene-catalysed 4- -2-cycloaddition of ketenes with 1-azadienes yielded optically active 3,4-dihydropyrimidin-2-ones (93% ee) ... 

An air-stable catalyst, prepared from dimer 1 and M-hetero-cyclic carbene (iVA -bis(2,6-diisopropylphenyl)4,5-dihydro-imidazol)-2-ylidene), afforded a-arylated ketones from aryl chlorides, bromides, or triflates (eq 87). The reaction conditions are compatible with aryl or alkyl methyl ketones. 

Employing a bifunctional enamine/metal Lewis acid catalyst enabled Wang and coworkers to perform a highly chemo-and enantioselective inverse-electron-demand hetero-Diels-Alder reaction of cyclic ketones with 8,y-unsaturated a-ketoesters (eq 12).21... 

Metalated cyclic aldo-nitrones are characterized by high reactivity toward electrophilic reagents. Reactions with aldehydes and ketones afford satisfactory yields of a-hydroxymethyl substituted derivatives of nitrones (551). The reactions were also carried out with a number of aliphatic, aromatic, and hetero-aromatic aldehydes and ketones (Schemes 2.124 and 2.125). 

In this Diels-Alder reaction with inverse electron demand the overlap of the LUMO of the 1-oxa-l,3-butadiene with the HOMO of the dienophile is dominant. Since the electron-withdrawing group of the oxabutadiene at the 3-position lowers its LUMO dramatically, both the cycloaddition and the condensation usually take place at room temperature. The reaction can be performed as a two-, three- or four-component transformation. There is actually no restriction on the aldehydes thus, aromatic, hetero-aromatic, saturated aliphatic and unsaturated aliphatic aldehydes may be used. In addition, ketones such as a-oxocarbocylic esters can also be employed. As 1,3-dicarbonyl compounds cyclic substances such as Meldrum s acid, barbituric acid and derivates, coumarines, any type of cycloalkane-1,3-dione and / -ketoesters, as well as their phosphorus, nitrogen or sulfur analogues and acyclic... 

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