Acyl migration esters

Acylated Corticoids. The corticoid side-chain of (30) was converted iato the cycHc ortho ester (96) by reaction with a lower alkyl ortho ester RC(OR )2 iu benzene solution ia the presence of i ra-toluenesulfonic acid (88). Acid hydrolysis of the product at room temperature led to the formation of the 17-monoesters (97) ia nearly quantitative yield. The 17-monoesters (97) underwent acyl migration to the 21-monoesters (98) on careful heating with. In this way, prednisolone 17a,21-methylorthovalerate was converted quantitatively iato prednisolone 17-valerate, which is a very active antiinflammatory agent (89). The iatermediate ortho esters also are active. Thus, 17a,21-(l -methoxy)-pentyhdenedioxy-l,4-pregnadiene-liP-ol-3,20-dione [(96), R = CH3, R = C Hg] is at least 70 times more potent than prednisolone (89). The above conversions... 

Abstract The photoinduced reactions of metal carbene complexes, particularly Group 6 Fischer carbenes, are comprehensively presented in this chapter with a complete listing of published examples. A majority of these processes involve CO insertion to produce species that have ketene-like reactivity. Cyclo addition reactions presented include reaction with imines to form /1-lactams, with alkenes to form cyclobutanones, with aldehydes to form /1-lactones, and with azoarenes to form diazetidinones. Photoinduced benzannulation processes are included. Reactions involving nucleophilic attack to form esters, amino acids, peptides, allenes, acylated arenes, and aza-Cope rearrangement products are detailed. A number of photoinduced reactions of carbenes do not involve CO insertion. These include reactions with sulfur ylides and sulfilimines, cyclopropanation, 1,3-dipolar cycloadditions, and acyl migrations. 

Transamination of barbiturate derivatives with semicarbazide Hydrolysis and acyl migration of corticosteroid esters Rate enhancement by CTABr depends on substrate structure Substrate micellization inhibits hydrolysis and acyl migration Reddy and Katiyar, 1981 Anderson el ai, 1983... 

The formation of tluorinated Q -hydroxy-jS-imino esters (180) by treatment of fluorinated imino ethers (179) with lithium 2,2,6,6-tetramethylpiperidide has been reported. A possible explanation for this interesting intramolecular rearrangement is proposed in Scheme 64. Acyclic imides derived from primary benzylic amines and amino acid esters have been found to undergo a novel nitrogen to carbon acyl migration via a base-generated carbanion to yield the corresponding a-amino... 

It is of interest that 197 rearranges to the 21-ester on heating, representing an O-to-0 acyl migration. 

Other Carboxylic Esters. Selective 2-0-acylation of sucrose has been achieved by way of the 2-oxyanion compound. Treatment of sucrose in DMF with 3-lauryl-, 3-stearyl-, 3-hydrocinnamoyl-, and 3-(4-phenylbutyryl)-thiazolidine-2-thione derivatives and sodium hydride produced the corresponding 2-0-acyl derivatives in good yield (69). Syntheses of 6-O-acylsucroses were also achieved by acylation with 3-acylthiazolidine-2-thione and 3-acyl-5-methyl-1,3,4-thiadiazole-2(3ff)-thione derivatives in the presence of sodium hydride in DMF, followed by acyl migration using l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or aqueous triethyl amine. 6-0-Acylsucroses were obtained directly when onlyDBU was used (70). 

Section IV,A,1 Attempts to prepare spiro-3i/-pyrazoIes from esters of 6-diazopenicillinic acid and l-phenyI-2-propyn-l-one resulted in spontaneous rearrangement to the isomeric l//-pyrazoIes via a unique migration of the 0-Iactam 6-7 bond.174 A similar spontaneous acyl migration was observed in the reaction between a 3-diazothiolan-4-one and DMAD.175... 

The bc portion (267) was synthesized (Scheme 19) by treatment of the ethyl ester of i3, 3-dimethyllevulinic acid with hot ethanolic ammonia, followed by pyrolysis to give (275). Meanwhile, treatment of /8, 8-dimethyllevulinic acid with thionyl chloride gave the butyrolac-tone (276), and the sodium salt of this was treated with (275) to give (277). Photochemically induced acyl migration gave (278), which was treated with methanolic ammonia subsequent dehydration afforded (279), which was then activated by O- ethylation with Meerwein s salt to give (267). 

The reaction of /V-cyclohexyl-/V-(2-pyridyl)carbodiimide and the allenic acid 83 in dry tetrahydrofuran at ambient temperature for 3 days afforded a 2 1 mixture of isomeric 2-oxo-2H- and 4-oxo-4/7-pyrido[l,2-a]pyrimid-ines 88 and 87 instead of the expected Diels-Alder adduct (92HCA1262). The formation of an activated ester 84 was suggested in the first step, which underwent a 1,5- or 1,3-acyl migration, giving rise to the isomeric pyrido(l,2-a]pyrimidines 87 and 88 via acylureas 85 and 86, respectively (Scheme 6). 

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