Selective Pivaloylation Research Articles

ChemInform Abstract: Selective Pivaloylation of Hydroxyl Groups by 3-Pivaloyl-1,3- thiazolidine-2-thione Under Neutral Conditions.

Abstract Under neutral conditions, 3-pivaloyl-1,3-thiazolidine-2-thione (PTT) was found to act as a selective pivaloylating reagent for hydroxyl groups. The primary hydroxyl groups of diols containing primary and secondary hydroxyl groups, and the phenolic hydroxyl groups of the diols having alcoholic and phenolic hydroxyl groups were selectively pivaloylated by PTT.

Hydroxy-Methoxybenzoic Methyl Esters: Synthesis and Antifeedant Activity on the Pine Weevil, Hylobius abietis

The pine weevil Hylobius abietis (L.) (Coleoptera: Curculionidae) feeds on the bark of coniferous seedlings and is the economically most important forestry restocking pest in large parts of Europe. Substances with an antifeedant effect may offer an environmentally friendly alternative to insecticides for the protection of planted seedlings. Bioassays were performed on commercial and synthetic methyl hydroxy-methoxybenzoates in order to determine their possible antifeedant activity. Two methyl hydroxy-methoxybenzoates were synthesized by esterification and mono-O-methylation of two dihydroxybenzoic acids. A regioselective protection-deprotection strategy was used in the synthetic pathway of the other non-commercial esters, esterification and selective pivaloylation of the less-hindered hydroxyl group of other commercial dihydroxybenzoic acids gave diester intermediates, which then were O-methylated before methanolysis of the pivaloyl group which yielded the desired non-commercial methyl hydroxy-methoxybenzoates. The five synthesized methyl hydroxy-methoxybenzoic esters were complemented with commercial samples of the five other isomers of methyl hydroxy-methoxybenzoate and spectrometric data were collected for the complete set of isomers. All ten isomers were tested for their antifeedant effect on the pine weevil. The effect varied considerably among the hydroxy-methoxybenzoic esters. Methyl 2-hydroxy-3-methoxybenzoate showed the highest effect and may thus be a candidate for practical use in pine weevil pest management.

New Highly Stereoselective Synthesis of ( E)-Droloxifene via Selective Protection of 3,4′-Dihydroxybenzophenone and McMurry Reaction

A new, highly stereoselective synthesis of ( E)-droloxifene is reported. Deprotection of 3,4′-dimethoxybenzophenone and selective pivaloylation of the 3′-phenolic position gave 4-hydroxy-3′-(trimethylacetoxy)benzophenone. A McMurry reaction between the preceding benzophenone and propiophenone gave the ( E)-olefin as a major product (14:1 E/ Z ratio in crude reaction), which was then alkylated with 2-dimethylaminoethyl chloride and deprotected to yield ( E)-droloxifene with a >100:1 E/ Z ratio (5 steps, 13%). Attempts to use this strategy as a suitable stereoselective method to obtain ( Z)-droloxifene were not successful.

The Synthesis of the 3′- and 3′′′-Monodeoxygenated Derivatives of β-Maltosyl-(1→4)-Trehalose

Two derivatives of β-maltosyl-(1→4)-trehalose monodeoxygenated at C-3′ or C-3′′′ have been synthesized in [2+2] block syntheses. Starting from 4,6;4′,6′-di-O-benzylidene-trehalose (3) the 3′-hydroxyl group was singled out by selective pivaloylation and reduced by a Barton-McCombie reaction. The benzylidene group in the vicinity of the deoxy function could be reductively opened to supply a suitable monodeoxygenated glycosyl acceptor (8). Standard glycosylation with hepta-O-acetylmaltosyl bromide and deprotection led to 3′-deoxymaltosyl-(1→4)-trehalose 13. For the synthesis of a 3′-deoxygenated derivative of maltose we used 1,6-anhydromaltose as starting material. From the tributyltin hydride reduction of the 3,3′-bis-thiocarbonylimidazole derivative 18, the 3′-monodeoxygenated derivative 20 was obtained in low yield. After opening of the 1,6-anhydro ring, the maltosyl derivative was activated as trichloroacetimidate 24. Glycosylation followed by standard deprotection furnished the 3′′′-deoxymaltosyl-(1→4)-trehalose 28.

Selective pivaloylation and diphenylacetylation of cyclomalto-oligosaccharides

Regioselective acylation of cyclomalto-oligosaccharides was achieved using pivaloyl and diphenylacetyl chlorides. The reaction of cyclomaltohexaose ( 1) with pivaloyl chloride gave the hexakis(2,6-di- O-pivaloyl) derivative 19 in 66% yield. Similar reaction with cyclomaltoheptaose ( 2) led to the octakis(2 I,6 II,6 III,6 IV,6 V,6 VI,6 VII- O-pivaloyl) 26 and the 17 heptakis(6- O-pivaloyl) derivatives in 34 and 26% yields, respectively. The octakis(6- O-pivaloyl) derivative 18 was the only compound isolated (72%) in the reaction of pivaloyl chloride with cyclomalto-octaose ( 3). Diphenylacetylation of 1–3 gave the symmetrical ( 20–22) and the non-symmetrical ( 27–29) per(6- O-diphenylacetyl) esters as major and minor products, respectively.

Syntheses of partially pivaloylated d-glucopyranoses: new substrates for the esterase from rabbit serum

The selective pivaloylation (pivaloyl chloride-pyridine) of d-glucopyranose proceeds by two pathways after initial 6-pivaloylation, namely, successive esterification of ( a) positions 1, 3, 4, and 2 (major pathway) and ( b) positions 2, 1, 4, and 3 (minor pathway). Numerous di- ( 3 and 4), tri ( 5–9), and tetra-pivalates ( 10–12) have been prepared and characterised. On treatment of the 2,6-dipivalate ( 4) with rabbit serum or partially purified esterase II, PivO-6 was hydrolysed selectively, whereas the 1,6-dipivalate ( 3) underwent partial 1 → 2 acyl migration to give 4 and enzymic de-esterification of 3 and 4 occurred simultaneously.

Selective pivaloylation of Hydroxyl Groups by 3-Pivaloyl-1,3-thiazolidine-2-thione Under Neutral Conditions

Under neutral conditions, 3-pivaloyl-1,3-thiazolidine-2-thione (PTT) was found to act as a selective pivaloylating reagent for hydroxyl groups. The primary hydroxyl groups of diols containing primary and secondary hydroxyl groups, and the phenolic hydroxyl groups of the diols having alcoholic and phenolic hydroxyl groups were selectively pivaloylated by PTT.

Syntheses of hepta-, hexa-, and penta-pivalates of trehalose by selective pivaloylation

The order of esterification of the eight hydroxyl groups of trehalose with pivaloyl chloride is HO-6,6′ > HO-2,2′ > HO-3,3′ > HO-4,4′. Under the appropriate conditions of pivaloylation, heptapivalates with either HO-4 or HO-3 free, hexapivalates with either HO-4,4′ or HO-3′,4 free, and pentapivalates with HO-3′,4,4′ free were obtained. In addition, selective pivaloyation of trehalose 2,2′,3,3′-tetrapivalate afforded the 4,4′-diol and the non-symmetrical 4,4′,6′-triol. The 4-ol, the major heptapivalate, was a convenient starting material for the syntheses of 4-azido-4-deoxy- and 4-amino-4-deoxy-trehalose, together with their 4-epimers, and 4-chloro-4-deoxy-α- d-galactopyranosyl α- d-glucopyranoside. The 4,4′,6′-triol was utilised as a synthetic precursor of 4,6-dichloro-4,6-dideoxy-α- d-galactopyranosyl 4-chloro-4-deoxy-α- d-galactopyranoside and its triazido and triamino analogues.

ChemInform Abstract: Selective Pivaloylation of 2‐Acetamido‐2‐deoxy Sugars.

ChemInformVolume 20, Issue 19 Natural Products ChemInform Abstract: Selective Pivaloylation of 2-Acetamido-2-deoxy Sugars. D. LJEVAKOVIC, D. LJEVAKOVIC Dep. Radioimmunol., Inst. Immunol., 41000 Zagreb, YugoslaviaSearch for more papers by this authorS. TOMIC, S. TOMIC Dep. Radioimmunol., Inst. Immunol., 41000 Zagreb, YugoslaviaSearch for more papers by this authorJ. TOMASIC, J. TOMASIC Dep. Radioimmunol., Inst. Immunol., 41000 Zagreb, YugoslaviaSearch for more papers by this author D. LJEVAKOVIC, D. LJEVAKOVIC Dep. Radioimmunol., Inst. Immunol., 41000 Zagreb, YugoslaviaSearch for more papers by this authorS. TOMIC, S. TOMIC Dep. Radioimmunol., Inst. Immunol., 41000 Zagreb, YugoslaviaSearch for more papers by this authorJ. TOMASIC, J. TOMASIC Dep. Radioimmunol., Inst. Immunol., 41000 Zagreb, YugoslaviaSearch for more papers by this author First published: May 9, 1989 https://doi.org/10.1002/chin.198919291AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume20, Issue19May 9, 1989 RelatedInformation

Selective pivaloylation of 2-acetamido-2-deoxy sugars

Selective pivaloylation of 2-acetamido-2-deoxy- d-glucose, its methyl α- and β-glycosides, and the methyl α-glycoside of N-acetyl- d-muramic acid under various conditions has been studied. The structures of the products were established by 1H-n.m.r. spectroscopy and acetylation. The orders of acylation, HO-6>HO-3>HO-1>HO-4 for 2-acetamido-2-deoxy- d-glucose and HO-6>HO-3>HO-4 for its methyl glycosides, were established. Methyl 2-acetamido-2-deoxy-3,6-di- O-pivaloyl-α- and -β- d-glucopyranosides and 2-acetamido-2-deoxy-1,3,4,6-tetra- O-pivaloyl- d-glucopyranose were hydrolysed by rabbit serum esterases.

ChemInform Abstract: Sucrochemistry. Part 33. The Selective Pivaloylation of Sucrose.

AbstractDie Reaktion von Sucrose (Ia) mit Pivaloylchlorid (II) ergibt in Abhängigkeit von den gewählten Reaktionsbedingungen die im Formelschema aufgeführten Derivatgemische.

Sucrochemistry. Part 33. The selective pivaloylation of sucrose

The pivaloylation of sucrose by pivaloyl chloride (2,2-dimethylpropanoyl chloride) has been studied under a variety of conditions and shown to be selective for certain hydroxy groups. There exists two principal, but divergent, reaction pathways lying between sucrose and its octapivalate in which the orders of acylation of the eight hydroxy groups are as follows (a) 6,6′-OH > 1′-OH > 4′-OH > 2-OH > 4-OH > 3′-OH > 3-OH; (b) 6,6′-OH > 1′-OH > 3′-OH > 3-OH > 4′-OH > 2-OH and 4-OH. With the exception of the 1′,3′,6,6′-tetra- and the 1′,2,3′,4,4′,6,6′-hepta-pivalate, all of the intermediary esters in these two reaction pathways have been isolated in yields in the range 30–52% depending upon the conditions employed.