. The photochemically induced conjugate addition of simple alcohols to a variety of a-enones has been investigated. With hex-2-enopyranosid-4-uloses (I), the alkylations occur from the less-hindered side and are completely stereo-and regioselective. The resulting 1,4-ketoalcohols (2) are readily cyclized to a-cyclopropyl ketones which have been prepared by alternative, less desirable routes. Alkylative additions of hex-1-enopyran-3-uloses occur also although less readily and without stereospecificity, giving C-glycosides. 2-Cyclohexenone and carvone are also photoalkylated by methanol giving moderate yields of the 1,4-ketols. In the case of carvone, carvone camphor was not detected as a by-product. Steroidal a-enones and mesityl oxide both fail to be photoalkylated by methanol. BERT FRASER-REID, NEVILLE LEWIS HOLDER, DAVID ROY HICKS et DAVID LOUIS WALKER.Can. J. Chem. 55,3978 (1977).L'addition conjuguee photochimiquement induite d'alcools simples a une variete d'knones-a est ttudiee. L'alkylation des hexeno-2 pyrannosiduloses-4 (1) a lieu sur le cBtC le moins encombre de la molkcule et est compl&tement stereo et rCgiosClective. Les c6toalcools-l,4 (2) resultants sont ensuite cyclises en a-cyclopropyl cttones lesquelles ont tte preparees par des routes moins desirables. L'addition par alkylation des hextno-l pyrannuloses-3 se produit aussi quoique moins facilement et sans stereospecificitk, conduisant B des C-glycosides. La cyclohexkne one-2 et la carvone sont aussi photoalkylCes par le methanol conduisant avec un rendement moyen aux cetols-1,4. Dans le cas de la carvone, la carvone-camphre n'est pas dttectte comme produit secondaire. Les Cnones-a dans la sCrie des stCroldes ainsi que I'oxyde de mksityle ne sont pas photoalkylts par le methanol.[Traduit par le journal]The ready availability in recent years of carbohydrate a-enones (1) has prompted the use of these versatile compounds in a variety of syntheses (see for example ref. 2). Conjugate-addition-alkylation of these enones offers simple access to biologically important branched-chain sugars, and hence we undertook an examination of a number of such reactions (3). In an accompanying paper (4) we report our results on the stereochemical course of copper-induced additerebic acid, Schenck et al. added isopropanol to maleic acid (6). The reaction has been of interest to photochemists (7) but prior to our own work (3) there was only oile recorded investigation of its synthetic utility (8), and the results therefrom were not encouraging. In this and the accompanying paper (5), it will be shown that the photoalkylation reaction is a simple and highly promising method of carbon-carbon bond formation. Experiments to determine some mechtion of organometallic reagents to some carbo-anistic as~ects of these reactions are currently hydrate enines. In this an; the following paper underwaGand will be reported in the future.---(5) we describe the photoinduced addition of oxycarbinyl species to these enone receptors.Additions to Alkyl Hex-2-enopyranosid-4-The photoinduced a...
Routes to methyl 3,4-dideoxy-a-D-glycero-hex-3-enopyranosidulose l a have been developed which use cheap readily-available chemicals, which are operable on a large scale and which have readily crystallizable materials as key intermediates (Scheme 4). Extensive use is made of reductive elimination of vicinal sulfonyloxy groups which is shown to operate equally well whether these groups on the pyranoside ring are in cis or tratls relationship. Contrary to other reported cases, it is found that the carbon-2 allylic hydroxyl goup is oxidized with manganese dioxide whether it is in pseudoaxial o r equatorial orientation.Differentes methodes utilisant des produits chimiques peu cohteux et facilement disponibles, pouvant facilement Ctre rentables a grande tchelle et irnpliquant des produits intermediaires facilement cristallisables, on CtC developptes afin d'obtenir le n~tthyl dideoxy-3,4 a-D-glycero hexeno-3 pyranosidulose l a (schema 4). Dans ces methodes, on a tres souvent utilist la reaction d'elimination rtductive des groupes sulfonyloxy vicinaux qui fonctionne bien, indtpendamment de la relation cis ou trans pouvant exister entre ces groupes sur l'anneau pyranosyde. Contrairement a ce qui a dtja tte rapporte dans d'autres cas. on a trouvt que le groupe hydroxyle allylique sur le carbone-2 est oxyde a I'aide du bioxyde d e manganese sans tenir compte de son orientation pseudoaxiale ou Cquatoriale.Can. .I. Chem., 51, 3357 (1973) [Traduit par le journal]
Whereas the pseudo-axial 3-hydroxyl group of allal derivatives is known to be inert to manganese dioxide oxidation, the equatorial counterpart in glucal derivatives is shown to be readily oxidized. Thus glucal is converted to the 6-O-triphenylmethyl ether or 6-O-benzoyl ester to promote solubility in chloroform, and the derivatives are oxidized in that solvent in 12 h or less.Acetonation of glucal is readily accomplished in 45 min using 2,2-dimethoxypropane and p-toluenesulfonic acid in dimethylformamide; the product may be oxidized directly either with manganese dioxide or dipyridine chromium oxide. Thus it is possible to obtain 1–3-g quantities of the crystalline acetonated enone from triacetyl glucal (via deacetylation, acetonation, and oxidation) in 3–4 h.If the acetonation medium stands for 2 h methyl 2,3-dideoxy-4,6-O-isopropylidene-α-D-erythro-hex-2-enopyranoside is obtained. The mechanism of its formation in the reaction medium is discussed.
3,4-Di-0-acetyl-D-xylal undergoes acid-catalyzed reaction with ethanol to give the anomeric mixture of ethyl 2,3-dideoxy-4-0-acetyl-~-glycero-pent-2-enopyranosides which can be separated after deacetylation.The a-D anomer 1 is readily oxidized by manganese dioxide to the a,p-unsaturated ketone but the p-D anomer 2 is inert. Thorough investigation of the 100 and 220 MHz n.m.r. spectra of 1 and 2, their acetates, and dinitrobenzoates indicates that each exists conformationally pure in the half-chair form having the benefit of the anomeric effect. Hence in the oxidizable anomer 1 the C-4 allylic hydroxyl group is pseudoequatorial; in the unoxidizable one it is pseudoaxial. Hydrogen bonding does not appear to be the reason for failure of 2 to oxidize.The ethoxy groups of 1 and 2 are found to be ABX, system with unusually large separation for the AB protons.Le di-O-acktyl-3,4-~-xylal soumis B une reaction acido-catalysee dans l'ethanol, donne un melange anomtrique de dideoxy-2,3-0-acetyl-4-D glyckro-pentene-2-pyranosides d'kthyle. L'isomere-a-D-1 est rapidement oxyde par le bioxyde de manganese en cetone or,p insaturee, par contre l'isornere P 2 est inerte. L'examen des composCs 1 et 2 iinsi que de leurs derives acetates et dinitrobenzoates, en r.m.n. 100 et 220 MHz a montrC que chacun des isomtres est exclusivement sous forme d'une dernie chaise gr%ce ii "l'effet anomkrique". Ainsi, I'isomere oxydC 1 possede line hydroxyle allylique en C-4 pseudo equatorial. Tandis que dans 2, le rn&me groupe est pseudo axial.Les groupes ethoxy dans 1 et 2 forrnent des systemes ABX, avec une separation inhabituellement grande des protons AB.Canadian Journal of Chemistry, 49,3038 (1971) In a recent publication from this laboratory (1) it was reported that when ethanol reacted with 3,4-di-0-acetyl-D-xylal under boron trifluoride catalysis (2) a mixture was produced which, after deacetylation, could be separated chromatographically into what appeared to be a-and P-anomers of ethyl 2,3-dideoxy-Dglycero-pent-2-enopyranoside. The faster running component l a behaved normally on manganese dioxide oxidation, being converted to an a,P-unsaturated ketone within 8 h. The slower running substance 2a, however, gave no evidence for ketone formation after 14 days of exposure to manganese dioxide.It seemed strange that l a and 2a would display such a difference in oxidizability if the only difference between both compounds was 'Undergraduate research participant, summer 1970. Department of Chemistry, University of Waterloo, Waterloo, Ontario. 2Revision received June 10, 1971. the orientation of the ethoxy group at the remote anomeric center. Both compounds characterized as their dinitrobenzoate esters l b and 2b respectively gave satisfactory microanalyses (3). As expected for an anomeric pair, both l a and 2a lost the aglycon readily (4) to give the same strong ion, 3, corresponding to M+-OCH,CH, at nz/e 99. Structure 4 which could also lead to ion 3 is excluded since 1 and 2 from their n.m.r. and i.r. spectra are not vinyl ethers. The speci...
Three triterpenes have been isolated from Cedrela odorata L. These are shown by chemical and spectroscopic evidence to be derivatives of tirucallol in which the side chain has been modified to a dihydroxytetrahydrofuran. , , 3312 cm.-l (OH) (Found: C, 75.9; H, 10-4; 0, 13.7. C30H5004 requires C, 75.9; H, 10.6; 0, 13.5%). Acetylation of the Cedrela Triterpenes.-This was done, in the standard way, with acetic anhydride and pyridine overnight a t room temperature. The products were isolated by dilution with water and filtration. Odoratol triacetate (V) was amorphous, v , , 1754 (OAc) cm.-l, 6 5.27 (lH, m, H-7), 5.12 (lH, q, J6.5 and 5.5 c./sec., H-23), 4-85 (lH, d, J 6.5 c./sec., H-24), 4-69 (lH, m, W J 5 c./sec., H-3), 4.02 (lH, d, J 5.5 c./sec., H-22), and 2.07 and 2.09 (6H and 3H respectively, each s, 3 x OAc) . Odoratone diacetate (11; R2 = Ac) gave needles, m.p. 222-224" (from methanol), vmx. 1754 (OAc) and 1710 (cyclohexanone) cm.-l, 6 5.34 ( l H , m, H-7), 5.13 ( l H , q, J 6-5 and 6.0 c./sec., H-23), 4.87 (lH, d, J -6.5 c./sec., H-24), 4.03 (lH, d, J 6.0 c./sec., H-22), and 2.08 and 2.11 (each 3H, s, 2 x OAc)
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