9-Borabicyclononane (9-BBN) has been utilized to protect functionalized amino acids for potential chemoselective side chain manipulation. The 9-BBN group imparts organic solubility to otherwise hydrophilic molecules and is tolerant of a wide range of reaction conditions. The high degree of solubility of these molecules in THF is particularly noteworthy. It is cleaved with either aqueous HCl or by exchange with ethylenediamine in methanol. [reaction: see text]

2,4-Dihydro-4-(beta-D-ribofuranosyl)-1,2,4(3H)-triazol-3-one (2) was identified as the principal phytotoxic component of a fermentation broth derived from an Actinomadura. The compound is a new natural product, but known by synthesis. Broad-spectrum herbicidal activity was demonstrated in greenhouse tests. Metabolite reversal studies suggested the target site was adenylosuccinate synthetase, which was confirmed by direct measurement of the activity of the 5'-phosphorylated derivative on the isolated enzyme.

Oxazaborolidinones 3, 25, 32, 42, 49, and 53 can be obtained as single diastereomers by crystallization-induced asymmetric transformation (AT). Asymmetric memory is maintained in the derived enolates because the stereogenic boron resists equilibration with achiral, trivalent boron-containing species on the time scale of enolate alkylation with methyl iodide, allyl bromide, or benzyl bromide. Conditions were found for alkylating oxazaborolidinone enolates derived from phenylalanine (5, 33), alanine (18, 26), phenylglycine (43), and valine (54) without significant loss of boron configuration. The phenylglycine-derived oxazaborolidinone alkylation products 44 and 45 slowly undergo boron epimerization at room temperature, and the C-allyl product 44b partially racemizes during hydrolytic cleavage, apparently by a 2-aza-Cope rearrangement. These complications were not encountered with phenylalanine derivatives. Preparatively useful results were obtained with oxazaborolidinones 3 and 32, derived from phenylalanine. AT favors a different boron configuration in the B-naphthyl analogue 32 compared to 3. This provides access to either quasi-enantiomeric enolate 5 or 33 by starting from the same phenylalanine enantiomer.

Synthesis of the novel natural product Phosphonothrixin has been accomplished in 6 steps and 24% overall yield from the commercially available Baylis-Hillman adduct derived from acetaldehyde and methyl vinyl ketone. The synthesis features use of a trisubstituted olefin as a latent a-hydroxyketone, which formally reverses the oxidation states of the hydroxyl and carbonyl functionalities. This alleviates some of the difficulties encountered in alternative syntheses which proceed through metastable intermediates.

Shake-flask cultures of Paecilomyces variotii produce a phytotoxin with high activity against broadleaf weeds and selectivity to corn. The phytotoxin was purified and identified as 14-hydroxycornexistin (2), a new member of the nonadride family.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Trimethylsilyldiazomethane converts maleic anhydride derivatives in alcoholic THF to bisesters. The highly acid and base sensitive natural product cornexistin was converted to its bis-methyl ester in 70–75% yield and to the mixed benzyl/methyl ester in 61% yield. The mixed ester can be converted back to cornexistin via transfer hydrogenation.

Reaction of ArB(OH)(2) (3) with KHF2 affords crystalline salts KArBF3 (2). In the presence of TMSCl in acetonitrile, 2a reacts to give NMR signals typical of PhBF(2) in acetonitrile solution. When the reaction of 2 + TMSCl is performed in the presence of potential Lewis bases, the trivalent borane 1 is intercepted, resulting in organoboron complexes. Thus, the oxazaborolidinones 7-10 have been prepared from amino acid-derived amidine carboxylates NaO2CCH(R)N = CHNMe(2) (R = H or phenyl). Complexes 11 and 12 derived from 1,3-diketones are also easily prepared. The KHF2 fluoride exchange coupled with the TMSCl activation method allows in situ generation of ArBF2 without having to handle corrosive trivalent boron halides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Amidine-protected oxazaborolidinones 6 and 7 can be made from Me(2)NCH=NCH(R '')CO2Na and KPhBF(3)/TMSCl. The diastereomers undergo equilibration and asymmetric transformation under conditions of crystallization, resulting in the formation of 6a and 6b with high diastereomer selectivity. Treatment of phenylalanine with ArB(CH3)OiPr (8) affords a 1:1 diastereomer mixture of the oxazaborolidinones 9 and 10. Crystallization affords a single diastereomer in high yield. These are all examples of asymmetric transformation of the ''second kind'' or ''second order'', abbreviated as AT. Crystallization of the less soluble diastereomer drives the equilibrium and results in nearly total conversion of the mixture. Interconversion of 9 and 10 occurs readily at room temperature (9a/10a) or upon mild heating(9b/10b). The latter system interconverts more slowly because the electron-withdrawing CF3 substituent stabilizes the ate complex. The B-fluoro derivatives 6 and 7 are also relatively stable, and interconversion requires warming. Rapid equilibration of diastereomers occurs when 9/10 is treated with triethylamine or other basic agents, probably due to the formation of 12 followed by C-O cleavage to 13. The N,N-dimethyl complexes 16 and 17 are prepared from 15 and KPhBF(3). Crystallization under AT conditions affords 16 as the favored diastereomer. Structure 16 equilibrates thermally with 17, but the process is not accelerated by added triethylamine. AT also takes place with high diastereomer selectivity in the case of the oxazaborolidinones 25 and 26. The relative stability of boron diastereomers in the crystal lattice is controlled by remote stereogenic carbons in a menthone-derived substituent.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA Simple Route to Unsymmetrically Substituted 1,2,4,5-TetrazinesStephen C. Fields, Marshall H. Parker, and W. Randal EricksonCite this: J. Org. Chem. 1994, 59, 26, 8284–8287Publication Date (Print):December 1, 1994Publication History Published online1 May 2002Published inissue 1 December 1994https://doi.org/10.1021/jo00105a059Request reuse permissionsArticle Views719Altmetric-Citations15LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (564 KB) Get e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Crystallization-assisted asymmetric transformation can be used to prepare single diastereomers of optically pure boron complexes (boroxazolidinones) from amino acids and KBF3. Conversion into enolates followed by alkylation results in optically pure alpha-alkyl amino acids after methanolysis of the boron complex.

ChemInformVolume 18, Issue 44 Heterocyclic Compounds ChemInform Abstract: α-Arylation of Pyrrolidinones. J. D. STEWART, J. D. STEWART Dep. Chem., Bucknell Univ., Lewisburg, PA 17837, USASearch for more papers by this authorS. C. FIELDS, S. C. FIELDS Dep. Chem., Bucknell Univ., Lewisburg, PA 17837, USASearch for more papers by this authorK. S. KOCHHAR, K. S. KOCHHAR Dep. Chem., Bucknell Univ., Lewisburg, PA 17837, USASearch for more papers by this authorH. W. PINNICK, H. W. PINNICK Dep. Chem., Bucknell Univ., Lewisburg, PA 17837, USASearch for more papers by this author J. D. STEWART, J. D. STEWART Dep. Chem., Bucknell Univ., Lewisburg, PA 17837, USASearch for more papers by this authorS. C. FIELDS, S. C. FIELDS Dep. Chem., Bucknell Univ., Lewisburg, PA 17837, USASearch for more papers by this authorK. S. KOCHHAR, K. S. KOCHHAR Dep. Chem., Bucknell Univ., Lewisburg, PA 17837, USASearch for more papers by this authorH. W. PINNICK, H. W. PINNICK Dep. Chem., Bucknell Univ., Lewisburg, PA 17837, USASearch for more papers by this author First published: November 3, 1987 https://doi.org/10.1002/chin.198744174Read the full textAboutPDF 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 onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume18, Issue44November 3, 1987 RelatedInformation