echemi logo
Product
  • Product
  • Supplier
  • Inquiry
    Home > Selective synthesis of 1,3-diene and 1,3,5-triene by Heck reaction of C-C bond breaking in JACS

    Selective synthesis of 1,3-diene and 1,3,5-triene by Heck reaction of C-C bond breaking in JACS

    • Last Update: 2018-10-31
    • Source: Internet
    • Author: User
    Search more information of high quality chemicals, good prices and reliable suppliers, visit www.echemi.com
    Substituted 1,3-diene is a kind of commonly used synthetic block, which can be used for various catalytic transformations, including asymmetric hydrogen functionalization, bifunctionalization, C-H functionalization, cycloaddition and cross coupling 1,3-diene is usually prepared by classical methods such as mizoroki Heck reaction, olefin metathesis or cross coupling (scheme 1) However, these methods also have some disadvantages, including poor compatibility between functional groups and strong alkaline organometallic reagents, and limited structural diversity of commercial raw materials Therefore, it is still necessary to develop a one-step catalytic route for the synthesis of substituted 1,3-dienes Recently, the Brad P Carrow group of Princeton University reported a mild palladium catalyzed aerobic heck coupling reaction of (hetero) arylboric acid or alkenylboric acid with cyclobutene, and synthesized substituted 1,3-diene or 1,3,5-triene in the way of region and stereo selection respectively Relevant articles were published on J am Chem SOC (DOI: 10.1021 / JACS 8b10007) (source: J am Chem SOC.) previous reports show that palladium catalyzed coupling reaction of arylhalides with butadiene has low yield, and competitive by-products of 1,4-diaryl-1,3-diene will be formed This is because the product 1-aryl-1,3-diene is more reactive than butadiene in the subsequent catalytic conversion Another problem is that stable (π - allyl) palladium intermediate will be formed after the reaction migration is inserted into butadiene, which is difficult to release diene (scheme 2, intermediate) through β - H elimination The author thinks that the above kinetic problems can be effectively avoided by using methylene cycloalkane instead of butadiene When methylenecycloalkanes migrate and insert, β - alkyl elimination breaks the tension ring, which may provide an alternative way for diene formation (scheme 2, top) Although Larock group has observed β - alkyl elimination in the reaction of anionic palladium complex, it has been transformed into the most stable π - allyl complex intermediate in thermodynamics It is speculated that electrophilic palladium complexes can solve the above problems, because they will form kinetic products in the process of oxidation of heck Then, the electrophilic organic palladium intermediate can react with cyclobutene through two possible C-C bond breaking pathways to form 1- substituted 1,3- diene without (π - Xi Bingji) palladium intermediate (Scheme 2, bottom) (source: J am Chem SOC.) therefore, the author studies the Heck reaction of boric acid to verify the above conjecture After a large number of screening of reaction conditions, the author determined the best conditions as follows: under oxygen atmosphere, Pd (OAC) 2 as catalyst, acetic acid and water as additives, 2-methyltetrahydrofuran as solvent, benzoboric acid and cyclobutene reacted at 45 ℃ for 72 hours, and trans-1-phenyl-1,3-butadiene 1 was obtained in almost quantitative yield (99%) The control experiment shows that the reaction can not take place with butadiene instead of cyclobutene or without palladium catalyst; the change of oxygen pressure, organoboron reagent type, additives and other conditions will reduce the yield (Table 1) (source: J am Chem SOC.) next, the author investigated the application range of various (hetero) aryl boric acids (Table 2) The yield of 1-aryl-1,3-diene (2,6,8,9 and 11-13) can be achieved in 56% - 91% of the aromatic boric acid with electron withdrawing substituents The coupling product (3 - 5) can be obtained in slightly lower yield (60% - 79%) from arylboric acid with electron donor 3-benzothiophene, 3 - (2-fluoro) pyridyl and 3 - (2,6-difluoro) pyridyl boric acid were also synthesized in medium yield (57% - 62%) to 1-heteroaryl-1,3-diene (14-16) It is found that the standard conditions for coupling arylboric acid with cyclobutene can also be directly applied to alkenylboric acid (Table 2) No competitive 6 π - electrocyclization products were observed during the reaction Cyclohexyl, tert butyl and chloropropyl substituted allylic boric acid can yield single stereoisomer (1E, 3e) - 1,3,5-triene (17-19) in good yield (63% - 72%) In addition, a variety of substituted trans styrylboric acids can successfully form (1E, 3e) - 1-aryl-1,3,5-triene (21-26) in 44% - 75% yield However, alkylboric acid (such as methyl, tert butyl, isopropyl, etc.) is not compatible with the reaction system (source: J am Chem SOC.) conclusion: Brad P Carrow group has developed a mild and universal synthesis route of 1-aryl-1,3-diene and substituted 1,3,5-triene This method complements the classical synthesis of 1,3-diene, and the commercial sources of organoboron reagents are extensive.
    This article is an English version of an article which is originally in the Chinese language on echemi.com and is provided for information purposes only. This website makes no representation or warranty of any kind, either expressed or implied, as to the accuracy, completeness ownership or reliability of the article or any translations thereof. If you have any concerns or complaints relating to the article, please send an email, providing a detailed description of the concern or complaint, to service@echemi.com. A staff member will contact you within 5 working days. Once verified, infringing content will be removed immediately.

    Contact Us

    The source of this page with content of products and services is from Internet, which doesn't represent ECHEMI's opinion. If you have any queries, please write to service@echemi.com. It will be replied within 5 days.

    Moreover, if you find any instances of plagiarism from the page, please send email to service@echemi.com with relevant evidence.