{"id":240459,"date":"2025-07-03T09:22:29","date_gmt":"2025-07-03T09:22:29","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=240459"},"modified":"2025-07-03T09:22:31","modified_gmt":"2025-07-03T09:22:31","slug":"the-diels-alder-reaction","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/07\/03\/the-diels-alder-reaction\/","title":{"rendered":"THE DIELS-ALDER REACTION"},"content":{"rendered":"\n

Stereoselective THE DIELS-ALDER REACTION: Synthesis of cis-4-Cyclohexene-1,2-dicarboxylic Anhydride SO2<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

The Correct Answer and Explanation is:<\/mark><\/strong><\/p>\n\n\n\n

Correct Answer<\/strong><\/p>\n\n\n\n

The reaction illustrates a two-step synthesis of cis-4-cyclohexene-1,2-dicarboxylic anhydride. The first step involves the thermal decomposition of 3-sulfolene in a retro-cheletropic reaction to generate 1,3-butadiene and sulfur dioxide gas. In the second step, the in situ generated 1,3-butadiene acts as a diene and undergoes a [4+2] Diels-Alder cycloaddition reaction with maleic anhydride, the dienophile, to yield the final bicyclic product with cis stereochemistry.<\/p>\n\n\n\n

Explanation<\/strong><\/p>\n\n\n\n

The chemical transformation shown is a classic and elegant example of the Diels-Alder reaction, a powerful method in organic chemistry for constructing six-membered rings. The overall synthesis is ingeniously designed in two distinct stages.<\/p>\n\n\n\n

The first stage addresses the practical challenge of handling 1,3-butadiene, which is a flammable gas at room temperature. Instead of using it directly, the reaction starts with 3-sulfolene, a stable and easy-to-handle solid. Upon heating, 3-sulfolene undergoes a retro-cheletropic reaction. This is a type of pericyclic reaction where two sigma bonds break, releasing a small, stable molecule. In this case, gaseous sulfur dioxide (SO2) is extruded, a process that is thermodynamically favorable and drives the formation of the reactive diene, 1,3-butadiene, directly within the reaction mixture, or in situ.<\/p>\n\n\n\n

The second stage is the core Diels-Alder reaction. The freshly generated 1,3-butadiene (the conjugated diene) immediately encounters maleic anhydride (the dienophile). The electron-rich diene and the electron-poor dienophile, activated by its two electron-withdrawing carbonyl groups, readily engage in a [4+2] cycloaddition. This concerted mechanism involves a cyclic flow of six pi electrons (four from the diene, two from the dienophile) to simultaneously form two new carbon-carbon sigma bonds and a new pi bond, creating the cyclohexene ring system.<\/p>\n\n\n\n

The reaction is stereoselective, which is a key feature of the Diels-Alder reaction. The geometry of the dienophile is preserved in the product. Since maleic anhydride is a cis<\/em>-alkene, the resulting anhydride ring fuses to the newly formed cyclohexene ring in a cis<\/em> fashion. The two hydrogen atoms on the bridgehead carbons are therefore on the same face of the ring, as depicted in the final product, cis-4-cyclohexene-1,2-dicarboxylic anhydride.thumb_upthumb_down<\/p>\n\n\n\n

\"\"<\/figure>\n","protected":false},"excerpt":{"rendered":"

Stereoselective THE DIELS-ALDER REACTION: Synthesis of cis-4-Cyclohexene-1,2-dicarboxylic Anhydride SO2 The Correct Answer and Explanation is: Correct Answer The reaction illustrates a two-step synthesis of cis-4-cyclohexene-1,2-dicarboxylic anhydride. The first step involves the thermal decomposition of 3-sulfolene in a retro-cheletropic reaction to generate 1,3-butadiene and sulfur dioxide gas. In the second step, the in situ generated 1,3-butadiene […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[25],"tags":[],"class_list":["post-240459","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/240459","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/comments?post=240459"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/240459\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=240459"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=240459"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=240459"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}