Pyrans, dihydro- from

Only little chemical and biological investigations have been conducted on acronycine derivatives modified at the 1 and/or 2 positions on the pyran ring. From a chemical point of view, previously described compounds modified at those positions only include bromo (7), nitro (8, 27), dihydro (361 (7, 27), and dihydronitro (8, 27) derivatives. 

Furfural — see Furan-2-oarbaldehyde, 532 Furfuryl acetate, o -(butoxycarbonyl)-anodic oxidation, 1, 424 Furfuryi acrylate polymerization, 1, 279 Furfuryl alcohol configuration, 4, 544 2-Furfuryl alcohol polyoondensation, 1, 278 reactions, 4, 70-71 Furfuryl alcohol, dihydro-pyran-4-one synthesis from, 3, 815 Furfuryl alcohol, tetrahydro-polymers, 1, 276 rearrangement, 3, 773 Furfuryl chloride reactions... 

Pyran, 3-chloro-3,4-dihydro-2,2-dimethoxy-synthesis, 3, 796-797 Pyran, 2-(chloromethyl)tetrahydro-5,10-pentadecadienol synthesis from, 1, 428 Pyran, 2-chlorotetrahydro-conformation, 3, 629 H NMR, 3, 579 Pyran, 4-chlorotetrahydro-synthesis, 3, 777... 

H-Pyran, 2-alkoxy-4-methyl-2,3-dihydro-conformation, 3, 630 4H-Pyran, 2-amino-IR spectra, 3, 593 synthesis, 3, 758 4H-Pyran, 4-benzylidene-synthesis, 3, 762 4H-Pyran, 2,3-dihydro-halogenation, 3, 723 hydroboration, 3, 723 oxepines from, 3, 725 oxidation, 3, 724 reactions, with acids, 3, 723 with carbenes, 3, 725 4H-Pyran, 5,6-dihydro-synthesis, 2, 91 4H-Pyran, 2,6-diphenyl-hydrogenation, 3, 777 4H-Pyran, 6-ethyl-3-vinyl-2,3-dihydro-reactions, with acids, 3, 723 4H-Pyran, 2-methoxy-synthesis, 3, 762 4H-Pyran, 2,4,4,6-tetramethyl-IR spectra, 3, 593 4H-Pyran, 2,4,6-triphenyl-IR spectra, 3, 593... 

Pyran-2-one, 5,6-dibromo-5,6-dihydro-reactions, 3, 735 Pyran-2-one, 5,6-dihydro-allylic bromination, 3, 799 dehydrogenation, 3, 724, 799 H NMR,3, 581 synthesis, 3, 841, 843 Pyran-2-one, 4,6-dimethyl-irradiation, 3, 677 photochemistry, 3, 678 Pyran-2-one, 5,6-dimethyl-chloromethylation, 3, 680 conformation, 3, 631 Pyran-2-one, 5-f ormyl-IR Spectra, 3, 595 Pyran-2-one, 6-formyl-IR spectra, 3, 595 Pyran-2-one, 5-halo-synthesis, 3, 799 Pyran-2-one, 3-hydroxy-IR spectra, 3, 595 Pyran-2-one, 4-hydroxy-methylation, 2, 57 3, 676 pyran-4-one synthesis from, 3, 816 reactions with phosphorus oxychloride, 2, 57 synthesis, 3, 792, 794, 795, 798 tautomerism, 2, 56 3, 642 Pyran-2-one, 4-hydroxy-6-methyl-methylation, 3, 692 reactions... 

Pyran-4-one, 2,2,5-trimethyl-2,3-dihydro-photodimerization, 3, 720 4H-Pyran-4-one, 2,3-dihydro-2,3,5-trimethyl-6-( 1 -methyl-2-oxobutyl)-synthesis, 3, 844 Pyranones alkylation, 2, 56 aromaticity, 3, 632, 633 C NMR, 3, 587, 635 H NMR, 3, 580 cardiac glycosides, 3, 883 chromone synthesis from, 3, 830 colour couplers... 

The oxa-Pictet-Spengler reaction has been used with success to prepare dihydrofurano[2,3-c]pyrans and isochromans from l-(3-furyl)alkan-2-ols and 2-(3 ,4 -dihydroxy)phenylethanol, respectively. Furanyl alcohol 32 reacted with isobutyraldehyde 33 in the presence of p-toluenesulfonic acid to give the corresponding CI5-5,7-diisopropyl 4,5-dihydro-7H-furano[2,3-c]pyran 34 in good yield. ... 

Dihydro-2f/-pyran-2-one has been prepared by reductive cycliza-tion of 5-hydroxy-2-pentynoic acid [2-Pentynoic acid, 5-hydroxy-], which is obtained in two steps from acetylene [Ethyne] and ethylene oxide [Oxirane] 3 and by the reaction of dihydropyran [277-Pyran, 3,4-dihydro-] with singlet oxygen [Oxygen, singlet].4,5 2ff-Pyran-2-one has been prepared by pyrolysis of heavy metal salts of coumalic acid [2//-Pyran-5-carboxylic acid, 2-oxo-],8 by pyrolysis of a-pyrone-6-carboxylic acid [211 - Pyran-6-carboxyl ic acid, 2-oxo-] over copper,7 and by pyrolysis of coumalic acid over copper (66-70% yield).8... 

The present one-step procedure for preparation of 5,6-dihydro-2if-pyran-2-one is slightly modified from that described in the original paper.9 It is simpler and easier than the three-step method3 used in the past and represents the most convenient synthesis presently available. The present preparation of 2f/-pyran-2-one has several advantages compared to the alternatives mentioned above simplicity of apparatus and technique, mild reaction conditions, availability of reactants, and ease of product isolation. 

The preparation of 5-ACETYL-l,2,3,4,5-PENTAMETHYLCYCLO-PENTADIENE is of value in the synthesis of pentamethyleyclo-pentadiene and many pentamethylcyclopentadienyl metal carbonyl derivatives that are more soluble in organic solvents than those derived from cyclopentadiene. Simple preparations of 5,6-DIHYDRO-2-PYRAN-2-0NE and 2-//-PYRAN-2-ONE make these hitherto rather inaccessible intermediates available for cycloaddition and other reactions. The already broad scope of the Michael reaction has been widened further by including an efficient preparation of ETHYL (E)-3-NITROACRYLATE. Workers in the field of heterocyclic chemistry will find a simplified method for the preparation of 2,3,4,5-TETRA-HYDROPYRIDINE of help. 

In connection with studies on the ring-opening polymerization of cyclic acetals, we have undertaken investigations on the polymerization of bicyclic acetals, bicyclic oxalactone, and bicyclic oxalactam, which yield polysaccharide analogs, macrocyclic oligoesters, and a hydrophilic polyamide, respectively, some of which can be expected to be useful as novel speciality polymers. The monomers employed in the studies were prepared via synthetic routes presented in Scheme 1, starting from 3,4-dihydro-2H-pyran-2-carbaldehyde (acrolein dimer) I. 

Polymerization of 6,8-dioxabicyclo[3.2.1]octane, 2, has been most extensively studied among bicyclic acetals. This monomer is readily prepared from 3,4-dihydro-2H-pyran-2-carbaldehyde 1 by reduction with sodium borohydride followed by add-... 

The same substrate (451) and 4-phenylhydrazono-3,4-dihydro-2//-l-benzo-pyran-2,3-dione (454) [prepared from the dione (452) with benzenediazo-nium chloride] gave 3-(o-hydroxy-a-phenyUiydrazonobenzyl)-2(l//)-quinox-alinone (455) (EtOH-AcOH, reflux, 90 min 80%). ... 

At least two derivatives of pyran have been used for the primary synthesis of quinoxalines. Thus o-phenylenediamine (390) and 6-(p-methoxyphenyl)-6-methyl-5,6-dihydro-2//-pyran-2,5-dione (391) in methylene chloride at 20°C open to the air for 48 h gave 3-[2-hydroxy-2-(p-methoxyphenyl)propionyl]methyl-3,4-dihydro-2(1 //)-quinoxalinone (392) (as a mixture of two stereoisomers) in 92% yield 488 the 3,4,4a,5,6,7,8,8a-octahydro analog was made similarly from 1,2-diaminocyclohex-ane (91% of two separable stereoisomers).488... 

Scheme 43) [92]. Reaction of dienophiles such as 4-nitrobenzaldehyde with linker 80 at high temperature gave Diels-Alder products. Dihydro-pyrans were released from the support by Bronsted or Lewis acid-nucleo-phile combinations in moderate to good yield with stereoselectivity for the anti isomer. 

Pyrano[3,2 ]indolizines such as 120 can be prepared from the reaction of N-( 1 -benzotriazolylmethyl)indolines with 3,4-dihydro-2//-pyran under acidic or Lewis-acidic conditions (Equation 26) <2001T4933>, and a simpler analogue 122 is the end product of an annulation process starting from the enamine 121 and ethyl acrylate <1996H(43)1391> (Scheme 34). Pyrano[4,3-/]indolizinetriones, for example, 124, result from the hydrolysis of protected 2,3-dihydro-l//-indolizincdioncs 123 (Equation 27) <2000H(53)771>. 

Pyranoindolizines can be prepared from iV-aryl-3-hydroxyisoindolones and 3,4-dihydro-2/7-pyran in a one-pot reaction in the presence of boron trifluoride etherate (Scheme 75) <2005TL5691>. 

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