Read more
Organic Synthesis International by Dr Anthony Melvin Crasto Ph.D, Worlddrugtracker, Million hits on google on all sites, One lakh connections worldwide. Pushing boundaries.Interaction site for Organic chemists worldwide, Mail me at amcrasto@gmail.com if you like me
Pages
- Home
- THESIS
- orgsyn.org site
- Chemspider synthetic pages
- ABOUT ME
- DISCLAIMER
- Montelukast and similar drugs
- Glitazar and glitazone series
- ABAN SERIES
- melteon series
- USEFUL LINKS
- LITERATURE SEARCH
- DIPINE SERIES
- International spaces
- GLIPTIN SERIES 2/2
- Atom Economy (AE), Reaction Mass Efficiency (RME) ...
Showing posts with label organic chemistry. Show all posts
Showing posts with label organic chemistry. Show all posts
Wednesday 13 November 2013
Asymmetric Esterification for Total Synthesis
Read more
Fine-Tuning Carboborations
Read more
Building Blocks to Sustainable Synthesis
Read more
Wednesday 25 September 2013
Turning to Site B
22-Azacholesterol is a novel inhibitor of smoothened that acts through an allosteric mechanism
Thursday 19 September 2013
Friday 6 September 2013
Selecting with Sulfur
Selecting with Sulfur
A method that selects between two products operates simply by changing the oxidation state of sulfur
Wednesday 21 August 2013
Organocatalytic 1,3-dipolar cycloaddition reactions of ketones and azides with water as a solvent
Green Chem., 2013, 15,2384-2388
DOI: 10.1039/C3GC41126E, Communication
DOI: 10.1039/C3GC41126E, Communication
*
Corresponding authors
a
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore
E-mail: chmwangj@nus.edu.sg ;
Fax: (+)65-6516-1691
E-mail: chmwangj@nus.edu.sg ;
Fax: (+)65-6516-1691
b
HuBei Collaborative Innovation Center of Non-power Nuclear Technology, Hubei University of Science and Technology, Hubei Province, China
First published online 22 Jul 2013
We reported an enamine catalyzed strategy to fully promote a 1,3-dipolar cycloaddition to access a vast pool of substituted 1,2,3-triazoles in water.
Graphene oxide as a facile acid catalyst for the one-pot conversion of carbohydrates into 5-ethoxymethylfurfural
Graphene oxide obtained by the Hummers method was discovered to be an efficient and recyclable acid catalyst for the conversion of fructose-based biopolymers into 5-ethoxymethylfurfural (EMF). EMF yields of 92%, 71%, 34% and 66% were achieved when 5-hydroxymethylfurfural (HMF), fructose, sucrose and inulin were used as starting materials, respectively.
Green Chem., 2013, 15,2379-2383
DOI: 10.1039/C3GC41109E, Communication
DOI: 10.1039/C3GC41109E, Communication
Hongliang Wang,ab Tiansheng Deng,a Yingxiong Wang,a Xiaojing Cui,ac Yongqin Qi,a Xindong Mu,d Xianglin Hou*a and Yulei Zhu*ac
*
Corresponding authors
a
Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, PR China
E-mail: houxl@sxicc.ac.cn ;
Fax: (+86) 351-4041153
E-mail: houxl@sxicc.ac.cn ;
Fax: (+86) 351-4041153
b
University of Chinese Academy of Sciences, Beijing, PR China
c
State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, PR China
d
Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, P. R. China
Monday 19 August 2013
PRINS REACTION
History
The original reactants employed by Dutch chemist Hendrik Jacobus Prins in his 1919 publication were styrene (scheme 2), pinene, camphene, eugenol, isosafrole and anethole.In 1937 the reaction was investigated as part of a quest for di-olefins to be used in synthetic rubber.
Reaction mechanism
The reaction mechanism for this reaction is depicted in scheme 5. The carbonyl reactant (2) is protonated by a protic acid and for the resulting oxonium ion 3 two resonance structures can be drawn. This electrophile engages in an electrophilic addition with the alkene to the carbocationic intermediate 4. Exactly how much positive charge is present on the secondary carbon atom in this intermediate should be determined for each reaction set. Evidence exists for neighbouring group participation of the hydroxyl oxygen or its neighboring carbon atom. When the overall reaction has a high degree of concertedness, the charge built-up will be modest.The three reaction modes open to this oxo-carbenium intermediate are:
- in blue: capture of the carbocation by water or any suitable nucleophile through 5 to the 1,3-adduct 6.
- in black: proton abstraction in an elimination reaction to unsaturated compound 7. When the alkene carries a methylene group, elimination and addition can be concerted with transfer of an allyl proton to the carbonyl group which in effect is an ene reaction in scheme 6.
- in green: capture of the carbocation by additional carbonyl reactant. In this mode the positive charge is dispersed over oxygen and carbon in the resonance structures 8a and 8b. Ring closure leads through intermediate 9 to the dioxane 10. An example is the conversion of styrene to 4-phenyl-m-dioxane.[4]
- in gray: only in specific reactions and when the carbocation is very stable the reaction takes a shortcut to the oxetane 12. The photochemical Paternò–Büchi reaction between alkenes and aldehydes to oxetanes is more straightforward.
Variations
Many variations of the Prins reaction exist because it lends itself easily to cyclization reactions and because it is possible to capture the oxo-carbenium ion with a large array of nucleophiles. The halo-Prins reaction is one such modification with replacement of protic acids and water by lewis acids such as stannic chloride and boron tribromide. The halogen is now the nucleophile recombining with the carbocation. The cyclization of certain allyl pulegones in scheme 7 with titanium tetrachloride in dichloromethane at −78 °C gives access to the decalin skeleton with the hydroxyl group and chlorine group predominantly in cis configuration (91% cis).[5] This observed cis diastereoselectivity is due to the intermediate formation of a trichlorotitanium alkoxide making possible an easy delivery of chlorine to the carbocation ion from the same face. The trans isomer is preferred (98% cis) when the switch is made to a tin tetrachloride reaction at room temperature.The Prins-pinacol reaction is a cascade reaction of a Prins reaction and a pinacol rearrangement. The carbonyl group in the reactant in scheme 8[6] is masked as a dimethyl acetal and the hydroxyl group is masked as a triisopropylsilyl ether (TIPS). With lewis acid stannic chloride the oxonium ion is activated and the pinacol rearrangement of the resulting Prins intermediate results in ring contraction and referral of the positive charge to the TIPS ether which eventually forms an aldehyde group in the final product as a mixture of cis and trans isomers with modest diastereoselectivity.
Uses
The Prins reaction is used in total synthesis of complex natural products, for example, in a key step of that of the synthesis of exiguolide:[7]External links
- Prins reaction in Alkaloid total synthesis Link
- Prins reaction @ organic-chemistry.org
References
- ^ Condensation of formaldehyde with some unsaturated compounds H. J. Prins, Chemisch Weekblad, 16, 64, 1072, 1510 1919
- ^ Chemical Abstracts 13, 3155 1919
- ^ The Olefin-Aldehyde Condensation. The Prins Reaction. E. Arundale, L. A. Mikeska Chem. Rev.; 1952; 51(3); 505–555. Link
- ^ 4-Phenyl-m-dioxane R. L. Shriner and Philip R. Ruby Organic Syntheses, Coll. Vol. 4, p.786 (1963); Vol. 33, p.72 (1953). Article
- ^ Syn- and Anti-Selective Prins Cyclizations of ,-Unsaturated Ketones to 1,3-Halohydrins with Lewis Acids R. Brandon Miles, Chad E. Davis, and Robert M. Coates J. Org. Chem.; 2006; 71(4) pp 1493 – 1501; Abstract
- ^ Scope and Facial Selectivity of the Prins-Pinacol Synthesis of Attached Rings Larry E. Overman and Emile J. Velthuisen J. Org. Chem.; 2006; 71(4) pp 1581 – 1587; Abstract
- ^ Total Synthesis of (+)-Exiguolide Min Sang Kwon, Sang Kook Woo, Seong Wook Na, and Eun Lee Angew. Chem. Int. Ed. 2008, 47, 1733–1735 doi:10.1002/anie.200705018
واکنش پرینز
واکنش پرینز واکنش پرینز (prins) یک واکنش آلی شامل افزایش الکتروفیلی یک آلدهید یا کتون به یک آلکن یا آلکین با گرفتن نوکلئوفیل است. نتیجه واکنش بستگی به شرایط واکنش دارد (طرح 1).در حضور آب و اسید پروتیک مانند سولفوریک اسید به صورت واسطه واکنش و فرمالدهید محصول واکنش یک 3و1- دی ال 3 است.زمانی که آب حضور ندارد آب زدایی برای تشکیل یک الکل آلیلی 4 اتفاق می افتد. با مقدار اضافی از فرمالدهید و دمای کم واکنش محصول واکنش یک دی اکسان 5 است. زمانی که
آب به وسیله استیک اسید جایگزین می شود استرهای مربوطه تشکیل می شود.
Subscribe to:
Posts (Atom)