Ketones, a-formyl

A diazo group can be introduced adjacent to a single carbonyl group indirectly by first converting the ketone to an a-formyl ketone (10-118), and then treating it with tosyl azide. As in the similar cases of 12-7 and 12-8, the formyl group is cleaved... 

Tetramethyl-1,3-diphenyl-2,4,6,8-tetraoxaadamantane (163, R = CH3) is made either by dimerization of an a-formyl ketone, such as a-formyl-isobutyrophenone, (164, R = CH3) with sulfuric acid186 or by dimerization of the aldehyde (165) with borontrifluoride etherate.187 The structure of the product was determined by PMR.186... 

The reaction was carried out with /3-keto esters, /3-diketones, malonate, a-formyl ketones, a-cyano and a-nitro esters, cyanoacetamide, and phen-ylsulfonylacetate. (PPh3)2PdCl2 was used with sodium phenoxide. Also, Pd(OAc)2 and PPh3 are good catalysts. When bidentate ligand was used, the 1 1 rather than 1 2 addition reaction took place (56). For example, bis(diphenylphosphino) 1,2-ethane (39) produced a mixture of the following 1,4- (59) and 1,2- (60) addition products ... 

Active methylene or methine compounds, to which two EWGs such as carbonyl, alkoxycarbonyl. formyl, cyano. nitro, and sulfonyl groups are attached, react with butadiene smoothly and their acidic hydrogens are displaced with the 2,7-octadienyl group to give mono- and disubstituted compounds[59], 3-Substituted 1,7-octadienes are obtained as minor products. The reaction is carried out with a /3-keto ester, /3-diketone, malonate, a-formyl ketones, a-cyano and a-nitro esters, cyanoacetamide, and phenylsulfonylacetate. Di(octadienyl)malonate (61) obtained by this reaction is converted into an... 

No benzofurans are obtained from substituted p-benzoquinones.389 The enamines of a-formyl ketones (AcOH, room temperature) with p-benzoquinone give 3-acyl-5-hydroxybenzofurans.390... 

Fig. 13.61. Acylation of a ketone enolate with a formic ester to generate a formyl ketone. The ketone enolate intermediate (not shown) is formed in an equilibrium reaction.

In general, the dehydrogenation of steroidal ketones is carried out in dry benzene or dioxane at reflux with 1.1 to 2 equiv. of the quinone. ) Similar conditions have also been used to prepare flavones, chromones" and spirodienones" in good yields (Table 6). Consistent with the apparent requirement that enolization is a prerequisite to dehyi genation with quinones,reactants such as a-formyl ketones, e.g. (37) and (38), that have a high enol content, dehydrogenate raindly at room temperature (Table6)."5- 6... 

A new annelation process involving photochemical cycloaddition of a-formyl ketones to symmetrical alkenes has provided alternative synthetic routes (Scheme 37) to valerane (385) and isovalerane (386) (cf. Vol. 5, p. 78 Vol. 6, p. 87). 

The reaction of enamines with iminium ions provides access to substituted j3 amino aldehydes and ketones (Scheme 61). In a similar manner the Mannich reaction gives access to oc,) -unsaturated aldehydes or -amino ketones (Scheme 62). Enamines undergo the Vilsmeier reaction to give a-formyl ketones Solvolysis of the Vilsmeier salt with aqueous or alcoholic sodium hydrogen sulphide produces an enamino thioaldehyde. The use of A-dichloromethylene-A,A -dimethylammonium chloride gives tertiary /5-ketoamides (Scheme 63). Iminoalkylation of enamines with nitrilium salts provides access to enamino ketones and j3-diketones (Scheme 64). 

The structures of the di-isoxazoles obtained from the di-a-formyl ketones (241) depended upon the reaction conditions hydroxylamine hydrochloride afforded the di-isoxazole (257) whilst hydroxylamine hydrate gave (242 X = O). Similarly, the unsaturated dichlorodialdehyde (258) gave (259) with hydroxylamine hydrochloride and (244 X = O) with the hydrate. 

Soft carbon nucleophiles, such as activated methylene or methyne compounds 11, react with butadiene to give a mixture of the mono- (12) and di-(2,7-octadienyl) adducts (13) in the case of = H (activated methylenes), and to give the monoadduct 12 in the case of activated methynes, as expected (Scheme 3). The addition reactions with various carbon nucleophiles, such as j8-keto esters, /S-diketones, malonate and malononitrile, a-formyl ketones and esters, a-cyano ketones and esters, cyanoacetoacetamide, phenyl-sulfonyl acetate,nitroalkanes, and an enamine, are summarized in Table 1. PdCl2(PPh3)2-NaOPh is often used as a catalyst for the dimerization reaction. Complexes... 

Reactions of silyl enol ethers with dialkoxycarbenium ions result in a-formyl ketones (eq 13), much like those achieved above through the use of enolate anions. With a dienol silane (eq 14), regioselective y-formylation is achieved. In extended alkenic systems, cationic cyclization (eq 15) can be realized. ... 

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