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Furans into pyrans

Ring contractions of pyran derivatives are occasionally valuable. The contraction of 3-halo-2-pyrones to 2-furoic acids under the influence of alkali has been studied and the conditions defined.58112113 The method is adaptable to the preparation of 3-furoic acid via furan-2,4-dicarboxylic acid58 and of 3,4,5-triphenylfuran-2-carboxylic acid.113 Another ring contraction involving halides is the conversion of 4-chloromethylpyrylium salts into furylmethyl ketones as indicated in Scheme 21.114 Pyridine oxides may be transformed with unexpected ease into furans through treatment with a thiol (Scheme 22).115... [Pg.189]

The reversal of the well-known transformation of sugars into pyrans has been detailed as a method for assembling simple monosaccharides from simple furans (71T1973). A compound of the 2-furylcarbinol type was converted by the Br2/MeOH procedure into a mixture of the cis and trans isomers of the corresponding 2,5-dimethoxy-2,5-dihydrofuran derivative (129). Mild acid hydrolysis of (129) resulted in cleavage of the acetal bonds with formation of the dicarbonyl compound (130) which underwent immediate cyclization to 2,3-dideoxy-DL-alk-2-enopyranos-4-ulose (131 Scheme 29). [Pg.426]

The conversion of furans into pyran-3(6//)-oncs can be achieved using hypervalent iodine compounds (95TL3553), whilst the pyranones undergo a base catalysed isomerisation to a hydroxycyclopent-2-enone (95CC1971). [Pg.282]

Alcohols are practically inert towards DIB at room temperature and react very slowly at elevated temperature, unless they possess special features. Thus, oxidation due to the presence of furan ring occurred in a series of furyl alcohols which with DIB alone or better in combination with magnesium perchlorate (in a molar ratio 1 2) were converted into pyran-3(6//)-ones [129]. [Pg.45]

Depending upon reaction conditions, the Pd-catalysed isomerisation of alkylidene cyclopropyl ketones can lead to furans or pyrans. In acetone and in the absence of added salts, proximal bond cleavage occurs exclusively and 4//-pyrans are formed <03AG(E)183>. The 4//-pyran unit has been spiro-linked into the indanoparacyclophanes <03T1739>. [Pg.406]

A number of naphtho[l,2-6]furan-6-ols, hetero-fused 1-naphthols, have been synthesised using the Stobbe condensation and converted into the furo[2,3-/]naphtho[l,2-6]pyran 54 by reaction with a propynol. Provided that an amino function is present in one of the 2,2-diaryl units, irradiation in toluene generates blue merocyanines, X,max 480 - 490 mn and 575 - 590 nm, which are strongly coloured and have half-lives of 30 - 60 s <03WOP025638>. The 8,9-methylenedioxy- and 8,9-ethylenedioxy-naphtho[l,2-6]pyrans have been obtained using the same methodology. They exhibit similar photochromic properties. [Pg.55]

Horton and coworkers have described an enol thioacetal-forming, elimination procedure starting from 2,3 4,5-di-0-isopropylidene-n-xylose diphenyl dithioacetal (246) leading to 2-deoxy-4,5-0-isopropylidene-D-tfireo-pent-l-enose diphenyl dithioacetal (247), which is, formally, a carbohydrate ketene derivative. Compound 247, obtained in a yield of 62%, is of potential interest for the preparation of various rare sugars. Treatment with acid converts it into derivatives of heteroaromatic compounds (furans and pyrans). [Pg.298]


See other pages where Furans into pyrans is mentioned: [Pg.148]    [Pg.376]    [Pg.468]    [Pg.148]    [Pg.148]    [Pg.138]    [Pg.91]    [Pg.691]    [Pg.844]    [Pg.108]    [Pg.691]    [Pg.237]    [Pg.91]    [Pg.844]    [Pg.61]    [Pg.170]    [Pg.174]    [Pg.700]    [Pg.61]    [Pg.311]    [Pg.311]    [Pg.312]    [Pg.299]    [Pg.857]    [Pg.110]    [Pg.16]    [Pg.364]    [Pg.1320]    [Pg.283]    [Pg.190]    [Pg.2610]    [Pg.170]    [Pg.174]   
See also in sourсe #XX -- [ Pg.30 , Pg.189 ]




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