4,6-bis -277-pyranone

However, in the presence of methanol the pyrandione (326) is the major product. This product is of course the cis isomer of the Michael adduct above and is considered to arise by isomerization of that species. The lower reaction temperature in the presence of solvent apparently favours isomerization at the expense of intramolecular cyclization (Scheme 94). A further product, formed in low yield in the absence of solvent, is the symmetrical bis-pyranone (327) which arises from a further Michael addition of the carbanion, this time at the sterically favoured 8-position of the enoate. 

Sharpless asymmetric oxidation of the meso 1,4-diol 10 results in its desymmetrisation to the pyran-3-one, which exists as a mixture with the dihydrofuran, and the doubly oxidised bis-pyranone. Each of these hemiacetals can be individually trapped in good yield by careful choice of reaction conditions <03OBC2393>. 

In transforming bis-ketone 45 to keto-epoxide 46, the elevated stereoselectivity was believed to be a consequence of tbe molecular shape — tbe sulfur ylide attacked preferentially from tbe convex face of the strongly puckered molecule of 45. Moreover, the pronounced chemoselectivity was attributed to tbe increased electropbilicity of the furanone versus the pyranone carbonyl, as a result of an inductive effect generated by tbe pair of spiroacetal oxygen substituents at tbe furanone a-position. ... 

Malonyl chloride reacted with boiling acetone to give the bicyclic 2 1 adduct 210 comprising a pyranone and a l,3-dioxan-4-one moiety (Scheme 99). The modest yield was compensated for by the ease of its preparation. Compound 210 bears a chloride which is almost as reactive as an acyl chloride and which can be substituted by various nucleophiles in a Stille coupling in modest yields <1997SL895>. Treatment of malonyl chloride with ketene and acetone at low temperature afforded symmetric bis(l,3-dioxin-4-ones) in 60% yield although a different reaction pathway may be assumed (Scheme 99) <2000TL4959>. 

A range of 2,2-bis(trifluoromethyl)-l,3-oxazepin-5-ones (334) has been prepared by the reaction of oxazolidin-5-ones with 1-diethylamino-l-propyne (75TL3223). l,3-Oxazepan-2-one has been prepared by the Beckmann rearrangement of tetrahydro-2-pyranone oxime. 

The complexation of pyranone to l,8-bis(dichloroboryl)-naphthalene has been investigated by Reilly and Oh. NMR and IR spectroscopy suggest that pyranone simultaneously coordinates to both Lewis-acidic centers in solution to form complex (181). In the presence of excess pyranone, a 2 1 complex with one pyranone molecule attached to each boron center is formed (Scheme 25). 

Various electrophiles bring about the cyclisation of o-(l-alkynyl)benzoates and (Z)-2-alken-4-ynoates to isocoumarins and pyran-2-ones in high yields extension to the synthesis of bis-coumarins and hetero-fused pyranones is successful (Scheme 25) <03JOC5936>. 3-Aryl-4-iodoisocoumarins, prepared in a similar manner, undergo Stille reactions and can readily be deiodinated <03T2067>. 

Bi- and tricyclic pyranones such as thio- and benzothiopyrano[4,3-6]-pyrans (78JHC181), pharmacologically active furo- and thieno[2,3-/i]-... 

The crystal structure of the bis-sulfone 16,18-diphenyl-3,ll-dithia[3]metacyclo[3](2,6)-pyrano-phan-17-one-2,2,l 1,11-tetraoxide (32) shows that the planar pyranone and benzene rings are tilted... 

Wang, W. (1991) Directed ortho and remote aromatic metalation synthesis of highly substituted biaryls, dibenzo(b,d)pyranones and 3,3 -substituted-l,l -bi-2-naphthols. M.Sc. Thesis. University of Waterloo, Canada. 

ClgH25N03 f 2,6-Bis(t-butyl)-3-dimethylcarbamoyl-4-pyranone, 45B, 344 Cl6H26 2r cis-4,4,8,8-Pentamethylene-2,6-dioxa-bicyclo[3.3.Oloctane, 42B, 246... 

Trifluoromethyl)-2-pyrone (65) was prepared in 65 % yield by reaction of 2-pyrone-6-carboxyUc acid with SF4-HF at 100 °C. Chloromethylation with bis(chloromethyl) ether and snlfuric acid at 75 °C gave an inseparable mixture of mono- and bis(chloramethyl)pyranones. However, when the mixture was treated with phenylcopper-dimethyl sulfide in THF at 35 °C, only 66 reacted, giving the desired pyrone 67 as one of the perspective inactivators of a-Chymotrypsin [30] (Scheme 22). 

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