Ketals synthesis

Synthetic Developments in Unsymmetrical Silyl Ketal Synthesis 2.1. Introduction... 

Bosch, J., Rubiralta, M and Moral, M., Man-nich cyclization involving the a-position of ketals Synthesis of 2-aryl-4-piperidones and 2-aryl-3-acyl-pyrrolidines, Heterocycles, 19,... 

Acetal and ketal synthesis. The combination of an acidic ion-exchange resin and a drying agent is also effective for synthesis of acetals and ketals."... 

Bromoadenosine monophosphate, 99 3-Bromo-2-butanone-l,4-diol diethyl ketal, synthesis of, 393, 394 Bromocolchicine, 567-571 binding to brain extracts, 570,571 synthesis of, 569 Bromoconduritol, 369,370 inhibition of glucosidase, 381 synthesis of, 380, 381 a-Bromo-ft>-(3-cyanophenyl)alkane, 122 6-Bromo-6-deo conduritol B epoxide, active site labeling, 377-380 3-Bromo-l,4-dihydroxy-2-butanone 1,4-bisphosphate, 142, 392, 396, 397 synthesis of, 392-395... 

The synthesis of polymethines with dimethylene bridges starts with aUcychc ketones (31), ketals (32), and enamines (X = NR2), or enol ethers (X = OR) (33). They possess two activated centers, methine or methylene groups, which react with Vilsmeief s reagent to produce the corresponding dyes. 

Interest in the synthesis of 19-norsteroids as orally active progestins prompted efforts to remove the C19 angular methyl substituent of readily available steroid precursors. Industrial applications include the direct conversion of androsta-l,4-diene-3,17-dione [897-06-3] (92) to estrone [53-16-7] (26) by thermolysis in mineral oil at about 500°C (136), and reductive elimination of the angular methyl group of the 17-ketal of the dione [2398-63-2] (93) with lithium biphenyl radical anion to form the 17-ketal of estrone [900-83-4] (94) (137). 

Pyrrole, 4-ethynyl-2-formyl-3-methyl-synthesis, 4, 222 Pyrrole, formyl-oxidation, 4, 289 reactions, 4, 292 with sulfoxides, 4, 293 synthesis, 4, 223, 274, 287 Pyrrole, 1-formyl-barrier to rotation, 4, 193 Pyrrole, 2-formyl-benzoylation, 4, 220 conformation, 2, 107 4, 193 diacetoxythallium derivative iodination, 4, 216 dipole moment, 4, 194 ketals, 4, 290 protonation, 4, 47 reactions... 

In a synthesis of sativene a carbonyl group was protected as a 2,4-DNP while a double bond was hydrated with BH3/H202/0H . Attempted protection of the carbonyl group as a ketal caused migration of the double bond protection as an oxime or oxime acetate was unsatisfactory since they would be reduced with BH3. 

In Sarett s total synthesis of cortisone, mild acid conditions were developed for the hydration of an ethoxyacetylenic carbinol to the ester without complete dehydration of the tertiary hydroxyl group. An acid-sensitive ketal group in another part of the molecule was also maintained. 

An ingenious approach to the synthesis of steroids incorporating a tropone A ring has been developed by Birch and co-workers. Addition of dibromocarbene to 3-methoxyestra-2,5(10)-dien-17-one 17-ethylene ketal (42) gives a monodibromocarbene adduct formulated as (43) accompanied by a minor amount of a bisadduct. This confirms earlier observations that electrophilic halocarbenes add mainly to 2,3- or 2,5-dihydroanisoles at the double bond bearing the methoxyl group. 

The synthesis of a large number of y-pyrones and y-pyranols from enamines has been brought about through the use of a wide variety of bifunctional molecules. These molecules include phenolic aldehydes (126,127), phenolic Mannich bases (128), ketal esters (129), and diketene (120-132). All of these molecules have an electrophilic carbonyl group and a nucleophilic oxygen center in relative 1,4 positions. This is illustrated by the reaction between salicylaldehyde (101) and the morpholine enamine of cyclohexanone to give pyranol 102 in a quantitative yield (127). 

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