Chemistry
Six Membered Ring
A six-membered ring is a cyclic organic compound that contains six carbon atoms in its ring structure. These rings are commonly found in many natural and synthetic compounds, including carbohydrates, amino acids, and steroids. The six-membered ring is an important structural motif in organic chemistry and is often used as a building block for the synthesis of more complex molecules.
Written by Perlego with AI-assistance
Related key terms
1 of 5
4 Key excerpts on "Six Membered Ring"
eBook - PDF- Ramesh Chandra, Snigdha Singh, Aarushi Singh(Authors)
- 2020(Publication Date)
- Arcler Press(Publisher)
The un-reactivity and the stability of, for example, a six-membered aromatic ring are linked with the presence of three pairs of electrons, which is known as pi (π) electrons. These pi electrons are linked with the three double bonds of the rings. All together, these kinds of electrons constitute the so-called aromatics sextet and develops an unusual stable structure that are linked with the aromatic ring as a complete, instead of, with the individual pairs of atoms. Along with this, heterocycles can also be categorized as aromatic, saturated, and unsaturated. In this way, as depicted in the below-mentioned formulas, the pyrrolidine is a saturated heterocyclic compound which is consisting of no double bond; 4,5-dihydrofuran is an unsaturated heterocyclic compound; and pyridine shows typical characteristic of heterocyclic Synthesis of Five- and Six-Membered Heterocyclic Compounds 213 aromatic, or heteroaromatic, substance. In the two structural formulas given for pyridine, the first shows the double bonds, on the other hand, the second represents the aromatic sextet with a circle. 7.4. GENERAL FEATURES OF HETEROCYCLIC COMPOUNDS The most common heterocycles are those who are having five-membered rings and six-membered rings and also are consisting heteroatoms of oxygen (O), nitrogen (N), or sulfur (S). The best known of the simple heterocyclic compounds are the furan, pyridine, thiophene, and pyrrole. A single molecule of pyridine is consisting of a ring of six atoms-five carbon atoms along with one atom of nitrogen. Molecules of furan, pyrrole, and thiophene, each of them is consisting of five-membered rings, which is made of four atoms of carbon and one atom of oxygen, one atom of nitrogen, and one atom of sulfur respectively. Pyrrole and pyridine are both nitrogen heterocycles and their molecules which are consisting of atoms of nitrogen along with the atoms of carbon in the rings.
eBook - ePub- Gordon Gribble, John A. Joule, Gordon W. Gribble(Authors)
- 2012(Publication Date)
- Elsevier(Publisher)
Chapter 6.4 Six-Membered Ring Systems: With O and/or S AtomsClementina M.M. Santos* , Artur M.S. Silva*** Department of Vegetal Production and Technology, School of Agriculture, Polytechnic Institute of Bragança, Bragança, Portugal** Department of Chemistry & QOPNA, University of Aveiro, Aveiro, PortugalE-mail address: [email protected]E-mail address: [email protected]AbstractThe review covers work published in the calendar year 2011. Novel reaction chemistry and new ring synthetic methods for pyrans, [1]benzopyrans, dihydro[1]benzopyrans (chromenes, chromans), [2]benzopyrans, dihydro[2]benzopyrans (isochromenes, isochromans), pyranones, coumarins, chromones, xanthenes, xanthones, thiopyrans, dioxins, dioxanes, trioxanes, tetraoxanes, dithianes, trithianes, and oxathianes are reviewed.Keywords• Pyrans • [1]Benzopyrans • Dihydro[1]benzopyrans (chromenes, chromans) • [2]Benzopyrans • dihydro[2]benzopyrans (isochromenes, isochromans) • Pyranones • Coumarins • Chromones • Xanthenes • Xanthones • Thiopyrans • Dioxins • Dioxanes • Trioxanes • Tetraoxanes • Dithianes • Trithianes • Oxathianes6.4.1 Introduction
The year 2011 was particularly rich in reviews involving the synthesis and transformations of a wide structural range of O - and S -6-membered heterocycles and some on their biological properties, reflecting their importance for the scientific community.An overview on the structure and biological activity of naturally occurring withanolides <11NPR705> and a review on structure, biological activity, and synthesis of plant polyphenols <11AGE586> , marine natural products <11NPR196 , 11NPR269> , and aromatic cyclopenta[c ]pyrans <11JHC747> have appeared. The synthesis of the various structural subcategories of limonoids has also been surveyed <11EJO19>
eBook - ePub- Gordon Gribble, J. Joule, Gordon W. Gribble(Authors)
- 2009(Publication Date)
- Elsevier(Publisher)
Chapter 6.4: Six-Membered Ring Systems: With O and/or S Atoms
John D. Hepwort (email: [email protected] )
University of Central Lancashire, Preston, UKB. Mark Heron (email: [email protected] )
Department of Colour Science, School of Chemistry, University of Leeds, Leeds, UK6.4.1. Introduction
2008 saw the publication of the third edition of Comprehensive Heterocyclic Chemistry and Volume 7 contains chapters on the structure and reactivity < 08CHECIII(7)337 >, synthesis < 08CHECIII(7)419 > and applications < 08CHECIII(7)701 > of pyrans and their benzo derivatives and on thiopyrans and their benzo derivatives < 08CHECIII(7)727 >. Chapters on 1,2-, 1,3- and 1,4-dioxins, -oxathiins, -dithiins and their benzo derivatives appear in Volume 8 < 08CHECIII(8)677 , 08CHECIII(8)739 , 08CHECIII(8)857 > and Volume 9 includes a chapter on six-membered rings with 1,2,4-oxygen and/or sulfur atoms < 08CHECIII(9)569 >. Other reviews which relate directly to topics in this chapter include those on C-O bond formation leading to 6-membered oxygenated heterocycles < 08T2683 >, Meldrum's acid in the synthesis of natural products < 08CSR789 >, the value of the Petasis-Ferrier union/rearrangement in the construction of cis-2,6-disubstituted tetrahydropyran units present in natural products < 08ACR675 >, cycloaddition reactions of 3-oxidopyrylium betaines < 08T3405 > and thiochroman-4-ones < 08JSC623 >. More general reviews which refer to pyrans, thiopyrans and related systems include coinage metal-assisted synthesis of heterocycles < 08CR3395 >, Pd-mediated intramolecular biaryl coupling < 08H(75)1305 >, organocatalysis < 08OBC2037 >, the Baylis-Hillman < 08T4511 > and Nazarov < 08CEJ9292 > reactions and multicomponent reactions of carbonyl compounds < 08S1 >.A simple route to benzannulated [5,6]spiroketals with potential in natural product synthesis involves heating 2-hydroxybenzyl acetates in neat 5-methylene-?-butyrolactone. The reaction proceeds via an o-quinone methide which undergoes a hetero Diels-Alder (HDA) reaction with the methylene unit (Scheme 1 ) < 08SL2500
eBook - PDFProgress in Heterocyclic Chemistry
A Critical Review of the 1993 Literature Preceded by Two Chapters on Current Heterocyclic Topics
- H. Suschitzky, E. F. V. Scriven(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
Chapter 6.4 Six-Membered Ring Systems: With O and/or S Atoms JOHN D. HEPWORTH and B. MARK HERON University of Central Lancashire, Preston, UK Introduction The importance of the pyran moiety in natural products such as polyether antibiotics and toxins (93CR1671) and pheromones (92MI367) ensures that a healthy interest is maintained in the area. Microbial pyran-2-ones and some reduced derivatives have been reviewed (93NPR71) and developments in the chemistry of beticolin (93TL1483), brevetoxin (93CC1638), halichondrins (93TL7541), milbemycin (93JCS(P1)1507, 93TL7479) and monensin (93JA7152, 7166) are illustrative. Naturally occurring fused derivatives and analogues which have received attention this year include cannabinoids (93T3291, 93TL5527), robustadials (93JOC6163), rotenoids (93JCS(P1)2591, 2605) and podophyllotoxins (93CC1200; 93JCS(P1)2533, 2541). Further studies on sulfur analogues of natural products include those on the 5-thiorotenoid system (93JCS(P1)2599) and on the podophyllotoxins (93T8073). 6.4.1 HETEROCYCLES CONTAINING ONE OXYGEN ATOM 6.4.1.1 Pyrans The chiral sultam-derived acetoacetyl equivalent (1) adds to arylidene-malononitriles in Michael fashion using piperidine as catalyst to give highly functionalised 4//-pyrans (2) in good yields and with good diastereoselectivity (93TL5627). H s Ar CN (i) piperidine, ^ s . V ^ CN PhMe, HO Ar () U A 1 H 4 H a C ^ N r ^ N H a (2) 271 272 Six-Membered Ring Systems: With O and/or S Atoms The cycloaddition of chiral vinyl ethers to the heterodiene methyl £-benzylidenepyruvate catalysed by Eu(fod)3 affords 3,4-dihydro-2//-pyrans in high yield and is regio- and endo-selective. Diastereofacial selectivity, a further attractive feature of this approach to these useful compounds, is observed when an alkoxycarbonyl function is a substituent at the chiral centre of the vinyl ether (93TA193).
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
