Monoket

The most commonly used protected derivatives of aldehydes and ketones are 1,3-dioxolanes and 1,3-oxathiolanes. They are obtained from the carbonyl compounds and 1,2-ethanediol or 2-mercaptoethanol, respectively, in aprotic solvents and in the presence of catalysts, e.g. BF, (L.F. Fieser, 1954 G.E. Wilson, Jr., 1968), and water scavengers, e.g. orthoesters (P. Doyle. 1965). Acid-catalyzed exchange dioxolanation with dioxolanes of low boiling ketones, e.g. acetone, which are distilled during the reaction, can also be applied (H. J. Dauben, Jr., 1954). Selective monoketalization of diketones is often used with good success (C. Mercier, 1973). Even from diketones with two keto groups of very similar reactivity monoketals may be obtained by repeated acid-catalyzed equilibration (W.S. Johnson, 1962 A.G. Hortmann, 1969). Most aldehydes are easily converted into acetals. The ketalization of ketones is more difficult for sterical reasons and often requires long reaction times at elevated temperatures. a, -Unsaturated ketones react more slowly than saturated ketones. 2-Mercaptoethanol is more reactive than 1,2-ethanediol (J. Romo, 1951 C. Djerassi, 1952 G.E. Wilson, Jr., 1968). 

The effect of the catalyst-steroid ratio has been studied for the p-toluene-sulphonic acid-catalyzed ketalization of androst-4-ene-3,17-dione. Selective formation of the 3-monoketal is observed with the use of an equimolar amount of ethylene glycol and a low ratio of catalyst to steroid. ... 

Selective removal of the C-20 protecting group of the bisketal (33) is effected by using boron trifluoride to produce the 3-monoketal (34). ... 

Thus cortisone 21-acetate (89) gives only the 3-monoketal (90) even under drastic conditions. ... 

Ethylenedioxy-2l-acetoxypregn-4-en-3-one A solution containing 3,3 20,20-bisethylenedioxypregn-5-en-21-ol acetate (120 mg) and /7-toluene-sulfonic acid hydrate (12 mg) in dry acetone (3 ml) is allowed to stand at 22° for 14 hr. Sodium bicarbonate solution and ether are added and the organic layer is separated, washed with water, dried and evaporated. Crystallization of the residue from hexane yields 81 mg (75%) of 20-monoketal, mp 140-141°. 

A solution of 10-cyano-3-monoketal (I) in 60 cc of dry ether and 60 ccof dry dioxane is dropped Into 400 cc of liquid ammonia. Then, 1.2 g of lithium in small pieces are introduced over a period of 90 minutes and the mixture is maintained under stirring until the blue color of the solution is discharged. 

Monocinque (Lusofarmaco) Monoket (Chiesi) Nitralfa (Malesci) Orasorbil (Rottapharm) dinitrate ... 

Imdur (Key Pharm.) Ismo (Wyeth-Ayerst) Monoket (Schwarz)... 

The monoketal of some diketones is formed in reasonable yield by the statistical method. Thus (3) gives a reasonable yield of (4) after separation from (3) and the bis-ketal, 64% of (4) can be isolated. ... 

However, it does not follow that in any individual case, the same applies. The monoketal (6) of the cyclic diketone (5) is much in demand as a synthetic intermediate and in conformational studies. Mono ketalisation is unsatisfactory here - very little of (6) can be isolated. This may be simply because the right conditions have not yet been found. Various solutions to this problem have been published I shall describe two, both based on the statistical method. 

Omura, K. Iodine oxidation of alpha -tocopherol and its model compound in alkaline methanol unexpected isomerization of the product quinone monoketals. J. Org. Chem. 1989, 54, 1987-1990. 

Although the Vilsmeier reaction is known best in aromatic systems, aliphatic olefins also undergo formylation. Synthesis of forwocortal (257) involves such a step. Formation of the monoketal of 255 involves the 3-ketone function with the familiar concomitant shift of the double bond to C-5,6. 

Porco s route to (—)-kinamycin C (3) began with 2,5-dihydroxybenzaldehyde (38), which was elaborated to the enone 35 by the sequence shown in Scheme 3.6. Regioselective bromination [25] followed by methylation and reduction of the aldehyde function afforded the primary alcohol 39. The alcohol 39 was dearomatized by treatment with bis(acetoxy)iodobenzene, to afford the quinone monoketal 41. Transketalization with 1,3-propanediol followed by silylation of the primary alcohol generated the silyl ether 42 in 72 % yield over three steps. 

Alkylidenecyclopentenediones.1 The adduct (2) of 1-lithiohexyne to the cy-clobutenedione 1 rearranges in the presence of Pd(OCOCF3)2 to alkylidenecyclopentenediones 3. A similar selective rearrangement obtains in rearrangements to 2-alkylideneindone-l,3-dione monoketals (equation I). In both cases the nonvinylic C-C bond (a) rearranges more rapidly. 

The reaction sequence outlined in Scheme 20.30 for the preparation of the chlorinated enyne-allenes was successfully adopted for the synthesis of the C44H26 hydrocarbon 251 having a carbon framework represented on the surface of C60 (Scheme 20.50) [83]. Condensation of the monoketal of acenaphthenequinone (243) with the lithium acetylide 101 afforded the propargylic alcohol 244. On exposure to thionyl chloride, 244 underwent a cascade sequence of reactions as described in Scheme 20.30 to furnish the chloride 248. Reduction followed by deprotection produced 250 to allow a repeat of condensation followed by the cascade transformation and reduction leading to 251. 

In the second instance, the electrochem-ically generated bromoquinone monoketal (90) was converted to the organolithium reagent (91) (Scheme 21) [46, 47]. Its reaction with ketal (92), a synthon for the 1,4-dipole (93) [49, 50], proceeded smoothly to afford, after sequential treatment with aqueous acid and boron tribromide, a 60% yield of a-dtromydnone (94). 

Tablets 10 and 20 mg Rx) Monoket (Schwarz Pharma), ISMO (Wyeth-Ayerst)...

Pregnancy Category C (nitroglycerin, isosorbide dinitrate, isosorbide mononitrate [ie, ISMO], amyl nitrite) Category B (isosorbide mononitrate ER [ie, Imdut], isosorbide mononitrate [ie, Monoket]). 

Nicolaou s synthetic plan (Scheme LVI) begins with c -bicyclo[3.3.0]octane-3,7-dione and proceeds after monoketalization to append the lower sidechain as in 62S... 

The approach to 731 developed by Dauben and Walker, outlined in Scheme LXXXII, begins with the Weiss-Cook condensation of 743 and proceeds after hydrolysis and monoketalization to furnish keto acid 744. Wolff-Kishner reduction, cycliza-tion, and methylation of this intermediate provided diketone 745 which was transformed by standard means to 746, a molecule which had previously been carried on to 731 (Scheme LXXX). 

Fig. 3.24 Oxidation of anisoles to p-benzoquinones monoketals catalysed by [Ru(CF3COO)2(Hp)(tmtacn)]+ [261]...

Brand Name(s) (isosorbide mononitrate) Imdur, ISMO, Monoket Cfiemical Class Nitrate, organic... 

Tablets 5 mg (ISDN, Isordil, IsordilTitradose), 10 mg (ISDN, ISMO, Isordil, IsordilTi-tradose, Monoket), 20 mg (ISDN, ISMO, Isordil, Isordil Titradose, Monoket), 30 mg (ISDN, Isordil, Isordil Titradose), 40 mg (ISDN, Isordil, Isordil Titradose). 

The voltammetric response of curcumin and carthamin must, in principle, be dominated by the oxidation of the phenol and/or methoxyphenol groups (see Scheme 2.2). The electrochemistry of methoxyphenols has claimed considerable attention because of their applications in organic synthesis [159-163]. As studied by Quideau et al., in aprotic media, 2-methoxyphenols are oxidized in two successive steps into cyclohexadienone derivatives [163], whereas a-(2)- and a-(4-methoxyphenoxy) alkanoic acids undergo electrochemically induced spirolac-tonization to develop synthetically useful orthoquinone bis- and monoketals. In the presence of methanol, the electrochemical pathway involves an initial one-electron loss, followed by proton loss, to form a monoketal radical. This undergoes a subsequent electron and proton loss coupled with the addition of alcohol to form an orthoquinone monoketal. The formal electrode potential for the second electron transfer... 

The principle of condensation with diketones has further been extended by using 1,3-diketones to form 2,4-disubstituted quinolizines.14 In general the reaction involves the condensation of 2-picolyllithium with the enol ether or the monoketal of a /3-dicarbonyl compound followed by cyclodehydration of the resulting carbinol by means of acid. This scheme is illustrated in Eq. (5). 

---