Stereospecific Claisen and intramolecular Diels-Alder reactions of chiral ester synthon 4 results in conversion of a single asymmetric center of commercially available ester 4 to a vitamin D synthon, the C/D cis Grundmann ketone 3. The addition of propenyllithium to aldehyde 9 was dominated by a chelated anti-Cram transition state and yielded the threo isomer 12a as the major product. The stereochemistry of 12a was determined by X-ray crystallography. Conversion of benzyl-protected erythro isomer 11b to its dimethylacryloyl ester followed by ester enolate Claisen rearrangement led to the C17 and C20 stereochemistry of vitamin D. Addition of a pentadienyl anion to aldehyde 15 gave a tetraene, 17, which underwent an intramolecular Diels-Alder reaction to produce compound 18. Removal of the C16 hydroxyl and hydrolysis gave only the cis-fused isomer of 3.

Der Silyl‐alkohol (Ia) liefert einen Ester (Ib), der zu (II) umgelagert und mit BF 3 zu (III) desilyliert wird.

Metallation of 3-vinyl-5-trimethylsilyl-1-pentene (16) with π-BuLi gives a Si substituted pentadienyl anion reagent for bisannelation of ortto-alkenyl benzaldehydes. Tricyclic olefin 23b produced by this method is a homo-allylsilane which undergoes protodesilylation to 4-vinyl-12-methoxy-18,19-bisnor-podocarpa-8,11,13-triene 24b. The addition of β-(trimethylsilyl)ethyl magnesium bromide (12) to 12-methoxy-18,19-bisnor-5β-podocarpa-8,11,13-triene-4-one 27 gave the corresponding alcohol 29. When 29 and related γ-hydroxy silanes are treated with acid, dehydration to allylsilane and protodesilylation to exocyclic vinyl compounds result. Alcohol 29 produces 24b in 93% yield. Compound 24b can be converted in several steps to podocarpic acid.

Metallation of 3-vinyl-5-trimethylsilyl-1-pentene (16) with π-BuLi gives a Si substituted pentadienyl anion reagent for bisannelation of ortto-alkenyl benzaldehydes. Tricyclic olefin 23b produced by this method is a homo-allylsilane which undergoes protodesilylation to 4-vinyl-12-methoxy-18,19-bisnor-podocarpa-8,11,13-triene 24b. The addition of β-(trimethylsilyl)ethyl magnesium bromide (12) to 12-methoxy-18,19-bisnor-5β-podocarpa-8,11,13-triene-4-one 27 gave the corresponding alcohol 29. When 29 and related γ-hydroxy silanes are treated with acid, dehydration to allylsilane and protodesilylation to exocyclic vinyl compounds result. Alcohol 29 produces 24b in 93% yield. Compound 24b can be converted in several steps to podocarpic acid.

Chemischer InformationsdienstVolume 12, Issue 46 Preparative Organic Chemistry ChemInform Abstract: ELIMINATION, FRAGMENTATION, AND PROTON TRANSFER IN 1,3-DITHIANES AND 1,3-DITHIOLANES IN THE GAS PHASE J. E. BARTMESS, J. E. BARTMESSSearch for more papers by this authorR. L. HAYS, R. L. HAYSSearch for more papers by this authorH. N. KHATRI, H. N. KHATRISearch for more papers by this authorR. N. MISRA, R. N. MISRASearch for more papers by this authorS. R. WILSON, S. R. WILSONSearch for more papers by this author J. E. BARTMESS, J. E. BARTMESSSearch for more papers by this authorR. L. HAYS, R. L. HAYSSearch for more papers by this authorH. N. KHATRI, H. N. KHATRISearch for more papers by this authorR. N. MISRA, R. N. MISRASearch for more papers by this authorS. R. WILSON, S. R. WILSONSearch for more papers by this author First published: November 17, 1981 https://doi.org/10.1002/chin.198146130AboutPDF 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. Volume12, Issue46November 17, 1981 RelatedInformation

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElimination, fragmentation, and proton transfer in 1,3-dithianes and 1,3-dithiolanes in the gas phaseJohn E. Bartmess, Robert L. Hays, Hiralal N. Khatri, Raj N. Misra, and Stephen R. WilsonCite this: J. Am. Chem. Soc. 1981, 103, 16, 4746–4751Publication Date (Print):August 1, 1981Publication History Published online1 May 2002Published inissue 1 August 1981https://pubs.acs.org/doi/10.1021/ja00406a014https://doi.org/10.1021/ja00406a014research-articleACS PublicationsRequest reuse permissionsArticle Views173Altmetric-Citations35LEARN 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 InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAlkoxide-promoted [1,3] rearrangements of 1,3-dithianesStephen R. Wilson, Raj N. Misra, and Gregory M. GeorgiadisCite this: J. Org. Chem. 1980, 45, 12, 2460–2468Publication Date (Print):June 1, 1980Publication History Published online1 May 2002Published inissue 1 June 1980https://doi.org/10.1021/jo01300a040Request reuse permissionsArticle Views340Altmetric-Citations16LEARN 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 (1 MB) Get e-Alertsclose Get e-Alerts

AbstractAus Methylencyclobutan (I) und BuLi wird die Li‐Verbindung (II) erzeugt und mit Elektrophilen wie CO2 (anschließende Veresterung), (V), (VIII) bzw. (XI) umgesetzt, wobei die regioisomeren Cyclobutene (III) und (IV), (VI) und (VII), (IX) und (X) bzw. (XII) und (XIII) gebildet werden.

Abstract3‐Methyl‐3‐butenol (Ia) wird in das Tosylat (Ib) umgewandelt und dann mit Lithiummethylmercaptid (II) zum Thioether (III) substituiert.

AbstractAufgrund röntgenographischer Kristalluntersuchungen wird dem aus der Pflanze Croton californicus isolierten Stoff die Struktur (I) (Barbasksäuremethylester) zugeteilt.

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