Chapter 6.4 - Six-Membered Ring Systems: With O and/or S Atoms
Introduction
The large number of reviews published in 2010 on a wide structural range of O- and S-6-membered heterocycles reflects their significance in many aspects of chemistry.
Reviews of marine natural products cover new compounds isolated 〈10NPR165〉 and synthesized 〈10NPR1186〉. More specific publications relate to polyether toxins with spiroimine rings 〈10EJO5743, 10NPR1350〉, ciguatoxin 〈10NPR1204〉, gambierol 〈10BCJ1401, 10CEJ7586, 10H(81)2203〉, and maitotoxin 〈10JA6855, 10JA9900〉. The use of SmI2-induced cyclizations 〈10CSR1955〉 and epoxide-opening cascades 〈10JOC2681〉 in ladder polyether synthesis has been discussed.
The isolation and synthesis of spiroketal natural products have been surveyed 〈10NPR1117, 10OBC29〉, developments in berkelic acid 〈10CEJ12133, 10OBC1284〉 and spirostrellolide 〈10CC3967, 10S505, 10T6597〉 synthesis have been described, and various aspects of spirodioxynaphthalenes, fungal secondary metabolites, have been reviewed 〈10NPR1840〉.
Pigments produced by fungi 〈10NPR1531〉, fungal natural products such as the pyrano-naphthoquinones 〈10OBC4793〉, the cyclization of fungal and bacterial aromatic polyketides 〈10NPR839〉, and strategies in the synthesis of fungal-derived benzopyran-containing indole alkaloids 〈10CSR591〉 have been discussed. A review of the engineered biosynthesis of plant polyketides has appeared 〈10TCC45〉.
The chemistry of black tea polyphenols 〈10NPR417〉, colour aspects of anthocyanins 〈B-09MI135, 09THC1〉, and naturally occurring phloroglucinols have been discussed 〈10NPR393〉.
Reviews on specific O-heterocycles include those on tetrahydropyrans 〈10T413〉, chromones 〈10JHC785〉, flavones 〈10NPR1571〉, naturally occurring caged xanthones 〈10CEJ9944〉, trioxane antimalarials 〈10ACR1444〉, and plants used for the treatment of malaria 〈10NPR961〉. Interest continues in coumarin- and xanthene-based fluorescent sensors as indicated by reviews on the detection of Zn2+ 〈10CSR1996〉 and CN− 〈10CSR127〉, on chemodosimeters 〈10CR6280〉, bioimaging 〈10CSR2048〉, and oligonucleotide conjugation 〈10CSR2054〉.
Discussions of specific reagents and reactions relevant to this chapter include those on Meldrum's acid 〈10ACR440〉, dimedone 〈09AHC1〉, asymmetric organocatalytic 〈10T2089〉, Pd-mediated 〈10H(81)517〉, and carbonylative Pd-catalyzed 〈10H(80)697〉 synthesis of O-heterocycles, catalytic asymmetric CH insertion reactions 〈10T6681〉, the Baylis–Hillman reaction 〈10CR5447〉, the Heck reaction 〈10H(81)1979〉, Pd-mediated O-bridged carbocycles 〈10H(81)1603〉, and metal triflates as catalysts 〈10SL2973〉.
Section snippets
Pyrans
In solvent-free conditions, the reaction of oxoalkyldithiocarbamates, isocyanides, and dimethyl acetylenedicarboxylate (DMAD) affords high yields of 2H-pyran-3,4-dicarboxylates 1 〈10T8464〉. Cyclohexanone-fused pyrans, for example, 2 also result from a Ph3P-catalyzed three-component reaction involving DMAD, dimedone, and carbonate derivatives 〈10HCA2218〉.
It is thought that a 4H-pyran is the initial product from the PPh3-catalyzed Michael addition of activated terminal alkynes to α,β-unsaturated
Thiopyrans and Analogues
A hDA reaction between fluorinated thioamides and 2,3-dimethylbutadiene carried out under microwave irradiation affords 2-amino derivatives of 2-perfluoroalkyl-3,6-dihydro-2H-thiopyrans 〈10TL990〉, and the first examples of 2-perfluoroalkylthiopyrylium salts have been obtained through the oxidative aromatization of 2H-thiopyrans 〈10TL6406〉.
α-Diazosulfones undergo an asymmetric Cu-catalyzed CH insertion that affords 2-acyltetrahydrothiopyran 1,1-dioxides 41 in only moderate yields but with high
Dioxins and Dioxanes
Endoperoxides can be isolated from the oxygenative photolysis of 1-methyl-9,10-anthraquinones and subsequently produce 1-hydroxymethylanthraquinones on reduction 〈10JOC412〉. Treatment of a carotenoid with FeCl3 in air affords a stable yellow cyclic hydroxy peroxide which undergoes a reversible change to the blue cationic polyene with water 〈10EJO4630〉.
The intramolecular insertion of a carbenoid into 3,6-dihydro-1,2-dioxines occurs preferentially into the peroxide linkage and leads to a mixture
Dithianes and Trithianes
Dilithiation of 9,9-di-n-octylfluorene followed by reaction with S8 affords the fluorene[4,5-cde][1,2]dithiine 50 which is oxidized by NBS/SiO2 to the thiosulfonate-bridged derivative 51 of potential as an end-capping reagent 〈10SL1333〉.
2-(Trimethylsilyl)-1,3-dithiane 1-oxide forms a ketene acetal on reaction with carbonyl compounds and subsequent hydrolytic cleavage of the dithiane unit yields the homologous carboxylic acid 〈10S2616〉. A Pummerer reaction of
Oxathianes
The o-thioquinone derived from the appropriately substituted o-hydroxy-N-thiophthalimide undergoes a hDA reaction with the phytone-derived pentadeca-1,3-diene 52 to produce 4-thiatocopherol (Scheme 64) 〈10EJO2218〉.
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Cited by (3)
The literature of heterocyclic chemistry, Part XII, 2010-2011
2014, Advances in Heterocyclic ChemistryCitation Excerpt :Triazines, tetrazines and fused ring polyaza systems: 09PHC(21)415 (2007), 09PHC(21)435 (2008), 11PHC(22)427, 11PHC(23)403. Six-membered ring systems with O and/or S atoms: 09PHC(21)455, 11PHC(22)449, 11PHC(23)427. Seven-membered rings: 09PHC(21)491, 11PHC(22)491, 11PHC(23)465.
Routes to xanthones: An update on the synthetic approaches
2012, Current Organic Chemistry