Intramolecular aldol-type condensation

Furthermore, the N-alkylation of 2-aminobenzyl alcohol 114 with ketones 115 in the presence of [IrCl(cod)]2 and KOH gave quinoline derivatives 116 (Equation 10.28) [52]. The reaction may be initiated by the formation of ketimine from 114 and 115, and the ketimine thus formed is oxidized by Ir catalyst and the 114 which serves as a hydrogen acceptor giving the corresponding aldehyde, which is eventually converted into quinoline 116 through intramolecular aldol-type condensation. 

Dithioacetals derived from heteropine 177 smoothly react with methylene iodide in the presence of a zinc-copper couple in refluxing ether to give the corresponding fused thiophenes 178. The suggested mechanism involves formation of an ylide which undergoes intramolecular aldol-type condensation assisted by coordination of zinc with a carbonyl followed by demethylation of the S-methylthiophenium species (Scheme 35 (1989TL3093)). 

Polymerizations of vinyl ketones such as methyl vinyl ketone are also complicated by nucleophilic attack of the initiator and propagating carbanion at the carbonyl group although few details have been established [Dotcheva and Tsvetanov, 1985 Hrdlovic et al., 1979 Nasrallah and Baylouzian, 1977]. Nucleophilic attack in these polymers results in addition, while that at the ester carbonyl of acrylates and methacrylates yields substitution. The major side reaction is an intramolecular aldol-type condensation. Abstraction of an a-hydrogen from a methyl group of the polymer by either initiator or propagating carbanion yields an a-carbanion that attacks the carbonyl group of the adjacent repeat unit. 

The reaction step of heterocyclization of iminocarbonyl compounds 136 is probably the rate-limiting stage, as for monocyclic pyrylium salts [82AHC(Suppl)]. Its rate is determined by the electrophilicity of the carbonyl group and by steric factors. In the case of a bulky 3-aryl group, especially with donor substituents, the rate of heterocyclization should be retarded, and because of this influence, the behavior of 136 becomes dependent on the nature of R3. Thus, if R3 = Me or Et, the possibility of intramolecular aldol-type condensation is real, and a-naphthylamines 140 are formed (82KGS552). 

Treatment of 131 with phosphorus oxychloride gave 126 (R = CH==CH—C6H3), presumably via an inter- or intramolecular aldol-type condensation followed by elimination to give an intermediate of type 132 which cyclizes.120 The same diazepine also has been obtained from 132.120... 

When 2-acetoxy-2-methylcyclopropyl hexyl ketone (11) was treated with sodium hydroxide in methanol, the cyclopentenone derivative dihydrojasmone (12) was obtained in good yield. It is assumed that the acetoxy group was hydrolyzed prior to the base-catalyzed cleavage reaction of the cyclopropanol derivative. Formation of the final product can be rationalized by an intramolecular aldol-type condensation. 

Sulfoxime arylation may be coupled with an intramolecular aldol-type condensation giving benzothiazines.108 After arylation of the sulfoxime 67 with an ortho-bromobenzaldehyde using catalytic Pd/BINAP, the product spontaneously condenses under the reaction conditions to give the cyclized product 69. Also, the enantiopurity of the starting sulfoximes 67 is maintained throughout the reaction course. 

When the autoxidation is carried out under basic conditions (t-BuOK/DMF), the initially formed ketoamides undergo intramolecular aldol-type condensation to give quinolinones in a preparatively useful process known as Winterfeldt oxidation [64]. 

When the thioacetal (128) was treated with allylmagnesium bromide and subsequently with BFs etherate, nucleophilic addition on the carbonyl carbon and a subsequent cationic cyclization took place the product (129) was obtained by aromatization with loss of methanethiol (Scheme 18) <84TL5095>. The reaction of (128) under the Simmons-Smith reaction conditions gave the thienothiepine derivative (130). The proposed mechanism for the formation of (130) involves a nucleophilic attack of the initially formed sulfonium ylide intermediate, intramolecular aldol type condensation, aromatization and demethylation (Scheme 19) <89TL3093>. 

The Knorr Pyrrole Synthesis. In this process, the starting materials are an alpha-amino ketone, or less commonly an alpha-amino aldehyde, and a beta-ketoester. In the latter, the protons on the alpha carbon are activated both by the keto and the ester carbonyls and are especially easily removed. The Knorr process starts with the condensation of the amino group with the keto group in the usual way to tie the two molecules together as in 4.29 of the example shown in Scheme 4.31. This species then undergoes intramolecular aldol-type condensation to form a reduced pyrrole derivative 4.30. 

A typical synthesis of allylrethrone, an important component of an insecticidal pyrthroid has been carried out by a combination of michael reaction of 5-nitro-l-pentene and methyl vinyl ketone in presence of Al Oj followed by an intramolecular aldol type condensation (Scheme 27). ... 

Trifluoromethylpyranopyrazole 121 reacted at C(6) atom with excess of methyl mercaptoacetate in the presence of triethylamine to form a derivative 122 of trifluo-romethyl thiophene bonded with a pyrazole fragment. The reaction took place via pyran ring opening and intramolecular aldol-type condensation [71],... 

A Michael reaction coupled with aldol-type condensation has been used in the one-pot synthesis of allylrethrone (Scheme 7.7), an important component of an insecticidal pyrethroid [32]. The conjugative addition of 5-nitro-l-pentene to methyl vinyl ketone is catalyzed by AI2O3 and occurs in the absence of solvent. An intramolecular aldol-type condensation is then carried out in alkaline aqueous medium after the conversion of the nitro group into a carbonyl by the Nef reaction. 

Aminobenzyl alcohol could be oxidatively cyclized with ketones catalyzed by a CUCI2 catalyst with a KOH base in dioxane at 100 C under O2 atmosphere to afford quinolines in good yields. When aldehydes were used as the substrates, the desired quinolines also could be obtained in two steps under the similar conditions. Intramolecular aldol-type condensation and cyclodehydration to form quinolone are involved for this transformation [153] (Scheme 8.83). 

Murai et al. in 1997 developed the carbonylation of aromatic imines for the preparation of indenones in the presence of Ru3(CO)j2 [10]. This process runs under 7 bar of ethylene and 5 atm of CO at 160 °C (Table 15.5). Control experiments demonstrated that one-pot two-step manner is involved first, the carbonylation of aromatic imines with CO and ethylene giving the keto imine and then the intramolecular aldol-type condensation of ketoimine would readily undergo to generate 1 in situ. Treatment of the crude reaction mixture with silica gel resulted in the elimination of ieri-butylamine from 1 and deliverance of the final product. 

Equilibria between hexa- and pentacoordinated sUicon complexes have been examined carefully by Kost et al. Exemplaiily the following works might be cited here Neutral hexacoordinated siUcon complexes derived from hydrazide chelating ligands with imino-donor groups form pentacoordinated Si complexes in the course of ionic dissociation reactions. Such complexes were shown to undergo facile intramolecular aldol-type condensation [176]. In a related system... 

Scheme 32 Intramolecular aldol-type condensation catalyzed by a chloride counterion...

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