{"id":14902,"date":"2015-11-23T11:33:43","date_gmt":"2015-11-23T11:33:43","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=14902"},"modified":"2023-07-04T16:18:02","modified_gmt":"2023-07-04T15:18:02","slug":"a-tutorial-problem-in-stereoelectronic-control-the-tiffeneau-demjanov-rearrangement-as-part-of-a-prostaglandin-synthesis","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=14902","title":{"rendered":"A tutorial problem in stereoelectronic control. The Tiffeneau-Demjanov rearrangement as part of a prostaglandin synthesis."},"content":{"rendered":"
\n

This reaction emerged a few years ago (thanks Alan!) as a tutorial problem in organic chemistry, in which students had to devise a mechanism for the reaction and use this to predict the stereochemical outcome at the two chiral centres indicated with *.  It originates in a brief report from R. B. Woodward’s group in 1973 describing a prostaglandin synthesis,[1]<\/a><\/span> the stereochemical outcome being crucial. Here I take a look at this mechanism using computation.<\/p>\n

\"TD\"<\/a><\/p>\n

The amino group is firstly converted to a diazonium chloride by nitrous acid and the resulting group is then easily eliminated. The problem is easy once you spot that either of the coloured bonds in the reactant is approximately antiperiplanar to the diazonium group, and might migrate to contract the ring. The green bond has a dihedral angle of ~174\u00b0 with respect to the C-N\u2261N bond whilst the red bond has a less optimal value of ~166\u00b0. This alignment can also be viewed using orbital overlaps, in this case the (localised) NBO corresponding to the green or red bond and the empty antibonding NBO for the C-N bond. Below, the blue phase of the C-C bond is presumed to overlap constructively with the purple phase of the C-N anti bond, and likewise for the red\/orange phases for the red bond.<\/p>\n

\"Click

Click for 3D<\/p><\/div>

\"Click

Click for 3D<\/p><\/div><\/p>\n

A transition state (\u03c9B97XD\/6-311G(d,p)\/SCRF=dichloromethane) can be located[2]<\/a><\/span> and this yields[3]<\/a><\/span> the reaction animation shown below;<\/p>\n

\"Ta\"<\/a><\/p>\n

This has lots of interesting features, itemised below. The essence of the mechanism is that the green bond is induced to migrate by the proton removal from the OH bond by the chloride group. The red bond, although also aligned more or less correctly, has no such assistance.<\/p>\n

    \n
  1. Plot 1<\/strong> of energy shows a small activation energy (7 kcal\/mol), leading to an exothermic reaction by about 34 kcal\/mol.<\/li>\n
  2. The gradient plot 2<\/strong> (the derivative of the energy with respect to the geometry) shows several interesting features\n
      \n
    1. The reaction starts at IRC = 1.5 with zero gradients.<\/li>\n
    2. It reaches the transition state very early (IRC=0.0), at which point the gradients are again zero.<\/li>\n
    3. and then the gradients (almost but not quite) reach zero again (IRC ~-2). This is called a hidden reaction intermediate<\/i> and corresponds to the cations noted above (as an ion pair, with chloride anion). Because the ion pair has a large dipole moment, one might expect the reaction to be sensitive to the polarity of any solvent, and these hidden intermediates might become real ones in highly polar solvents.<\/li>\n
    4. At IRC -5, the gradients become large as the carbon starts to migrate.<\/li>\n
    5. The migration (with retention<\/b> of stereochemistry, it is a cationic [1,2] sigmatropic shift) is induced by the chloride anion starting to abstract the proton from the OH group, in synchrony with the carbon migration.<\/li>\n
    6. After IRC -8, we see only conformational<\/b> changes occurring, which may also be interesting to analyse.<\/li>\n<\/ol>\n<\/li>\n
    7. Plot 3<\/strong> shows the length of the breaking (migrating) C-C (green) bond. It hardly changes up to the transition state; it is only afterwards that it really starts to break\/migrate. Curiously, the red bond actually lengthens more than the green one at this stage (watch the animation above carefully) before changing its mind and reforming.<\/li>\n
    8. Plot 4<\/strong> the length of the newly forming (migrating) C-C bond. Note how initially, up to the transition state, this bond also lengthens<\/em> (rather more than the green one does), before slowly reversing itself to contract at the transition state after IRC -3.<\/li>\n
    9. Plots 5 and 6<\/strong> show the lengths of the O…H and Cl…H bonds as the proton transfer proceeds. This mostly occurs AFTER the transition state is passed, and so the reaction should not exhibit any primary kinetic isotope effect induced by e.g.<\/i> deuterium substitution.<\/li>\n
    10. Plot 7<\/strong> shows the dipole moment evolving along the reaction. At the start the species is an ion pair (diazonium chloride), but as the reaction proceeds HCl is formed and the dipole moment decreases to that of a less ionic compound.<\/li>\n<\/ol>\n

      \"TSE\"<\/a><\/p>\n

      \"TSG\"<\/a><\/p>\n

      \"TSBL12\"<\/a><\/p>\n

      \"TSBL13\"<\/a><\/p>\n

      \"TSBLOH\"<\/a><\/p>\n

      \"TSBLClH\"<\/a><\/p>\n

      \"TSDM\"<\/a><\/p>\n

      As a learning tool, I find such animations carry a lot of information about reactions and their mechanism and it does not take more than a day or so to chart their course in the manner above.<\/p>\n

      References<\/h2>\n
      1. R.B. Woodward, J. Gosteli, I. Ernest, R.J. Friary, G. Nestler, H. Raman, R. Sitrin, C. Suter, and J.K. Whitesell, \"Novel synthesis of prostaglandin F2.alpha.\", Journal of the American Chemical Society<\/i>, vol. 95, pp. 6853-6855, 1973. https:\/\/doi.org\/10.1021\/ja00801a066<\/a>\n\n<\/li>\n
      2. H.S. Rzepa, \"C 8 H 13 Cl 1 N 2 O 4\", 2015. https:\/\/doi.org\/10.14469\/ch\/191625<\/a>\n\n<\/li>\n
      3. H.S. Rzepa, \"C8H13ClN2O4\", 2015. https:\/\/doi.org\/10.14469\/ch\/191626<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

        This reaction emerged a few years ago (thanks Alan!) as a tutorial problem in organic chemistry, in which students had to devise a mechanism for the reaction and use this to predict the stereochemical outcome at the two chiral centres indicated with *.  It originates in a brief report from R. B. Woodward’s group in […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"activitypub_content_warning":"","activitypub_content_visibility":"","activitypub_max_image_attachments":5,"activitypub_interaction_policy_quote":"anyone","activitypub_status":"","footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[4,1086],"tags":[693,152,24,1593],"ppma_author":[2661],"class_list":["post-14902","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry","category-reaction-mechanism-2","tag-activation-energy","tag-animation","tag-energy","tag-learning-tool"],"yoast_head":"\nA tutorial problem in stereoelectronic control. The Tiffeneau-Demjanov rearrangement as part of a prostaglandin synthesis. - Henry Rzepa's Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=14902\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"A tutorial problem in stereoelectronic control. The Tiffeneau-Demjanov rearrangement as part of a prostaglandin synthesis. - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"This reaction emerged a few years ago (thanks Alan!) as a tutorial problem in organic chemistry, in which students had to devise a mechanism for the reaction and use this to predict the stereochemical outcome at the two chiral centres indicated with *.  It originates in a brief report from R. B. Woodward’s group in […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=14902\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa's Blog\" \/>\n<meta property=\"article:published_time\" content=\"2015-11-23T11:33:43+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2023-07-04T15:18:02+00:00\" \/>\n<meta property=\"og:image\" content=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2015\/11\/TD.svg\" \/>\n<meta name=\"author\" content=\"Henry Rzepa\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Henry Rzepa\" \/>\n\t<meta name=\"twitter:label2\" content=\"Estimated reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"4 minutes\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"A tutorial problem in stereoelectronic control. 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Stereochemistry galore.","author":"Henry Rzepa","date":"April 4, 2013","format":false,"excerpt":"Back in the days (1893) when few compounds were known, new ones could end up being named after the discoverer. Thus Feist is known for the compound bearing his name; the 2,3 carboxylic acid of methylenecyclopropane (1, with Me replaced by CO2H). Compound 1 itself nowadays is used to calibrate\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"methylene-cyclopropane","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/04\/methylene-cyclopropane.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":14944,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=14944","url_meta":{"origin":14902,"position":1},"title":"A tutorial problem in stereoelectronic control. A Grob alternative to the Tiffeneau-Demjanov rearrangement?","author":"Henry Rzepa","date":"November 28, 2015","format":false,"excerpt":"In answering tutorial problems, students often need skills in deciding how much time to spend on explaining what does not happen, as well as what does. Here I explore alternatives to the mechanism outlined in the previous post to see what computation\u00a0has to say about what does (or might) not\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"Alt1","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2015\/11\/Alt1.gif?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":23281,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=23281","url_meta":{"origin":14902,"position":2},"title":"The Stevens rearrangement: how history gives us new insights.","author":"Henry Rzepa","date":"January 29, 2021","format":false,"excerpt":"In a recent post, I told the story of how in the early 1960s, Robert Woodward had encountered an unexpected stereochemical outcome to the reaction of a hexatriene, part of his grand synthesis of vitamin B12. He had constructed a model of the reaction he wanted to undertake, perhaps with\u2026","rel":"","context":"In "Historical"","block_context":{"text":"Historical","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=565"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/01\/sden.jpg?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":16441,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=16441","url_meta":{"origin":14902,"position":3},"title":"An alternative mechanism for nucleophilic substitution at silicon using a tetra-alkyl ammonium fluoride.","author":"Henry Rzepa","date":"May 27, 2016","format":false,"excerpt":"In the previous post, I explored the mechanism for nucleophilic substitution at a silicon centre proceeding via retention of configuration involving a Berry-like pseudorotation.\u00a0Here\u00a0I probe an alternative route involving inversion of configuration at the Si centre. Both stereochemical modes are known to occur, depending on the leaving group, solvent and\u2026","rel":"","context":"In "reaction mechanism"","block_context":{"text":"reaction mechanism","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1086"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":12895,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=12895","url_meta":{"origin":14902,"position":4},"title":"Computationally directed synthesis: 2,3-dimethyl-2-butene + NO(+).","author":"Henry Rzepa","date":"September 6, 2014","format":false,"excerpt":"In the previous posts, I explored reactions which can be flipped between two potential (stereochemical) outcomes. This triggered a memory from Alex, who pointed out this article from 1999 in which the nitrosonium cation as an electrophile can have two outcomes A or B when interacting with the electron-rich 2,3-dimethyl-2-butene.\u2026","rel":"","context":"In "pericyclic"","block_context":{"text":"pericyclic","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=559"},"img":{"alt_text":"NOa","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2014\/09\/NOa.gif?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":12880,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=12880","url_meta":{"origin":14902,"position":5},"title":"Full circle. Stereoisomeric transition states for [1,4] pericyclic shifts.","author":"Henry Rzepa","date":"August 18, 2014","format":false,"excerpt":"This post, the fifth in the series, comes full circle. I started off by speculating how to invert the stereochemical outcome of an electrocyclic reaction by inverting a bond polarity. This led to finding transition states for BOTH outcomes with suitable substitution, and then seeking other examples. Migration in homotropylium\u2026","rel":"","context":"In "pericyclic"","block_context":{"text":"pericyclic","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=559"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"jetpack_likes_enabled":false,"authors":[{"term_id":2661,"user_id":1,"is_guest":0,"slug":"admin","display_name":"Henry Rzepa","avatar_url":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","0":null,"1":"","2":"","3":"","4":"","5":"","6":"","7":"","8":""}],"_links":{"self":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/14902","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=14902"}],"version-history":[{"count":21,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/14902\/revisions"}],"predecessor-version":[{"id":26198,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/14902\/revisions\/26198"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=14902"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=14902"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=14902"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=14902"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}