Synthesis of 5-Substituted Pyrimidines<sup>1</sup>

Asbun, Wady; Binkley, S. B.

doi:10.1021/jo01345a032

Cited by 34 publications

(14 citation statements)

References 2 publications

(2 reference statements)

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“…The synthetic plan is shown in Scheme . We planned to use d -xylose derivative 45 as the starting material and anticipated that allylboration of this aldehyde with geranylboronate 46 would diastereoselectively provide homoallylic alcohol 47 , which possesses a quaternary stereocenter. After introduction of the benzoic acid moiety, arylated olefin 48 could be converted into alkenyl bromide or terminal alkyne 49 .…”

Section: Resultsmentioning

confidence: 99%

Stereoselective Synthesis of the Tricyclic Core of (−)-Callophycoic Acid A

et al. 2020

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Two stereocontrolled routes to the tricyclic core of (−)-callophycoic acid A are described. Our synthetic strategy relied on stereoselective allylboration using a new allylboronate reagent to construct the all-carbon quaternary stereocenter in the core, followed by efficient radical cyclization or palladium-catalyzed reductive cyclization to form its multisubstituted cyclohexane ring. The tetrahydrooxepin ring was constructed by intramolecular etheration. This study provides the first method for the stereoselective synthesis of the characteristic tricyclic skeleton of callophycoic acids.

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Section: Resultsmentioning

confidence: 99%

Stereoselective Synthesis of the Tricyclic Core of (−)-Callophycoic Acid A

et al. 2020

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“…[4] [2,4-Bis(benzyloxy)pyrimidyl-5-yl]lithium was set free analogously from 2,4-bis(benzyloxy)-5-bromopyrimidine. [5] The yields of products obtained upon trapping with standard electrophiles such as carbon dioxide or aldehydes were moderate (20-50 %) and did not significantly improve when pylamide before being allowed to react with dry ice. In contrast, consecutive treatment of 2-bromo-4-(trifluoromethyl)-pyrimidine and 2-chloro-5-iodo-4-(trifluoromethyl)pyrimidine with butyllithium affords the expected carboxylic acids in only poor yields and not even trace amounts of acid were detected when 4-bromo-6-(trifluoromethyl)pyrimidine served as the substrate.…”

Section: Introductionmentioning

confidence: 98%

Metal‐Bearing and Trifluoromethyl‐Substituted Pyrimidines: Generation and Functionalization

2006

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Keywords: Functionalization / Halogen/metal permutation / Metalation / Nucleophilic addition / Pyrimidines / Single electron transfer / Trifluoromethyl groups 5-Pyrimidyllithium species are fairly stable when the metal is flanked by two electron-withdrawing substituents such as trifluoromethyl and chlorine or bromine. Thus, the corresponding 5-carboxylic acids are produced in high yields from 4,5-dibromo-6-(trifluoromethyl)pyrimidine and 5-bromo-4-chloro-6-(trifluoromethyl)pyrimidine upon halogen/metal permutation accomplished with isopropylmagnesium chloride or butyllithium followed by carboxylation. Satisfactory or excellent yields of 5-carboxylic acids are equally obtained when 4-chloro-, 2,4-dichloro-and 2,4-dibromo-6-(trifluoromethyl)pyrimidine are deprotonated with lithium diisopro-

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“…The hydrogens of the number two methylene group can exist in four such conformations with the hydroxyl group on carbon number three. Fisher-Taylor-Hirschfelder models show that neither of the two conformations [one staggered (8), one eclipsed ( 9) ] which might lead to an initial cis double bond exhibit severe steric crowding; much more severe steric interactions do occur with the two conformations (10,11) leading to the trans double bond, particularly with the meso isomer of the pinacol. Furthermore, in a stepwise conversion of the pinacol to the dienes with the first double bond being trans, the intermediate, ¿rans-3,4-dimethyl-4-hexen-3-ol, has much more severe steric interactions than does its cis isomer; this factor alone would strongly favor the formation of the initial double bond with a cis configuration.…”

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confidence: 99%

“…The reaction of the mixture of the dienes with sulfur dioxide provided chemical evidence for the assignment of the trans-trans structure to the isomer of uv max 205 µ. Butadiene and one of the piperylenes react with sulfur dioxide to form cyclic sulfones. 8 The diene must be in the cisoid form for this reaction to occur, and it is known that the reaction with sulfur dioxide can be slowed down or prevented by a terminal methyl group in the position where the sulfur dioxide must approach.8 Accordingly, it would be expected that the trans-trans 4, with two methyl groups blocking the approach of the sulfur dioxide, would not react. This was found to be the case; most of the isomer assigned the trans-trans structure was still present unreacted after standing for 10 days with sulfur dioxide at -17°.…”

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confidence: 99%