Benzyl oximes

The reactions shown below were used in a synthesis of perhydrohistrionicotoxin the carbonyl groups were protected as an oxime and an O-benzyl oxime. ... 

Die Reaktion von Formaldehyd-(O-benzyl-oxim) mit einem Alkyl-lithium bei tiefer Tem-peratur fiihrt zum N-Lithium-Derivat eines N-Alkyl-O-benzyl-hydroxylamins, das bei der Umsetzung mit einem weiteren Alkyl-lithium das N-Lithium-Derivat eines Dialkylamins ergibt dieses wird ohne Isolierung mit einem Alkyl-halogenid zu einem Trialkylamin al-kyliert1. 

Intermolecular reactions between 0-benzyl oximes and ketones (or aldehydes) are limited to those with formaldehyde O-benzyl oxime. However, intramolecular coupling proceeds with carbonyl-tethered oxime ethers (Equation (69)). 

The second synthesis of lasubine II (6) by Narasaka et al. utilizes stereoselective reduction of a /3-hydroxy ketone O-benzyl oxime with lithium aluminum hydride, yielding the corresponding syn-/3-amino alcohol (Scheme 5) 17, 18). The 1,3-dithiane derivative 45 of 3,4-dimethoxybenzaldehyde was converted to 46 in 64% yield via alkylation with 2-bromo-l,l-dimethoxyethane followed by acid hydrolysis. Treatment of the aldol, obtained from condensation of 46 with the kinetic lithium enolate of 5-hexen-2-one, with O-benzylhydroxylamine hy-... 

The mercury(II)-induced cyclization of the m-2,6-disubstituted piperidine 10, prepared by selenium-induced cyclization of the unsaturated 0-benzyl oxime followed by reduction of the intermediate cyclic iminium salt251 (Section 7.2.6.2.6.), occurred efficiently and diastereoselectively (NOE). 

Interestingly, the stereochemistry of the hydroxyl group on the imino nitrogen in oxime 10 affects the stereochemistry of hydroxylamine 11 (see Scheme 9.4). Thus, hydride reduction of either (Z)- or (E)-oximes 10 with hydroborane in the presence of chiral amino alcohols produces (S)- and (R)-A-benzyl oximes 11, respectively, as shown in the table in Scheme 9.4, which were subsequently transformed to (R)-and (S)-trifluoroalanine 12 [14]. 

Microwave irradiation of ketoxirnes on wet silica-supported NaBiOj produces the original ketones within a few minutes [270]. The deoximation of allylic and benzylic oximes can also be achieved by use of Zn(BiO3)2 [271]. 

While tin reagents have provided ample methods for the generation of anomeric radicals, the variety of structures useful as radical acceptors is extremely diverse. In addition to the conjugated nitriles and conjugated carbonyl compounds, oximes have also been used. As shown in Scheme 5.2.14, Hart, et al.,22 effected a C-glycosidation utilizing an O-benzyl oxime and a tin reagent. The reaction proceeded in 80% yield with a anomeric selectivity. 

Table 24 Condensation Reactions of Silyl Ketene Acetals (219) and O-Benzyl Oxime Ethers (220)...

Table 23 -Lactam-forming Reactions of O-Benzyl Oxime Ethers (214) and Enolates of Ester (213)IN...

Deoximation. The conversion seems to be limited to allylic and benzylic oximes. 

O-benzyl-oximes with lithium aluminium hydride in the presence of... 

Recent syntheses of indol-2-ones (oxindoles) include Chuang s p-toluenesulfo-nyl radical induced cyclization of allylsulfones and the oxidative free-radical reactions of a,a-dimethylsulfonyl substituted anilides [62], the tin-free synthesis of 3-aminoindolinones from O-benzyl oxime substituted amidocyclohexadienes [63], and Pudlo s 5-exo-trigl5-exo-trig tandem radical cyclization of acrylamides to give 3-pyrrolidinone substituted oxindoles, shown below [64]. 

To a suspension of 77.7 mg 4-amino-l-(3,4-dihydroxy-5-hydroxymethyltetra-hydrofuran-2-yl)-lH-pyrimidin-2-one 3-oxide (cytidine -oxide, 0.30 mmol) and 12.6 mg 95% pure lithium hydride (1.5 mmol) in 5 mL dry methanol was added 40 /xL 98% pure benzyl bromide (0.33 mmol) the mixture was stirred at 37°C for 1 day under an argon atmosphere. TLC analysis of the reaction mixtures with chloroform/methanol/acetic acid (16 6 3) and chloroform/methanol (10 1) as the developing solvents showed complete consumption of the starting material for almost quantitative conversion to a less polar compound. After being neutralized with 1 N HCl solution and subsequent removal of the solvent under reduced pressure, the resulting residue was subjected to a short silica gel column by eluting with chloroform/methanol (20 1) to isolate 99.5 mg l-(3,4-dihydroxy-5-hydroxymethyltetrahydrofuran-2-yl)-17/-pyrimidin-2,4-dione 4- 0-benzyl oxime (uridine 4-0-benzyloxime) as a colorless amorphous powder, in a yield of 95%, m.p. 123-125°C (from methanol). 

The formyl group in 13 was used to construct the piperidine A ring. Thus, once 13 was converted into an O-benzyl oxime, a hydroboration— oxidation reaction led to alcohol 14. Protection of the hydroxy group withp-methoxybenzyl chloride also caused the eHmination of the O-benzyl oxime moiety to give a nitrile, which was then reduced to the primary amine 15. 

Oxidation of the dibutylstannylene derivative of methyl 3, 4 -0-isopropylidene-a-lactoside with bromine in acetonitrile in the presence of tributyltin methoxide led specifically to the 2-ketone isolated as its o-methyl or Q-benzyl oxime, whereas the corresponding 0-lactoside derivative gave the 3-ketone selectively. Microbial oxidation of toluene (using Pseudomonas putida 39D) gave the cis-diol (1), which after Q-protection and ozonolysis afforded the chiral pentosuloses (2). Photochemical... 

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