Synthetic applications of the photochemically induced addition of oxycarbinyl species to α-enones. Part I. The addition of simple alcohols

Abstract

. 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...

Carbohydrate Derivatives in the Asymmetric Synthesis of Natural Products

“…The structure of the latter was readily deduced from the pmr spectrum in which H -1 appeared as a doublet J 12 = 4.0 Hz. This value, which is uncharacteristically large for trans-diequatoriaI' protons (see Scheme 4), is usually observed when a trigonal centre is present at C-4 (25). Accordingly reduction with lithium aluminum hydride gives the diol (185) in which J12 < I Hz.…”

“…Selective sulfonylation of the primary hydroxyl group precedes formation of the oxirane (25). These reactions preserve the chirality at C-5 of (25) as does the succeeding regio-specific cleavage leading to (26).…”

“…The sequence (Scheme 40) that had worked so well (25) for the preparation of the simple cyclopropyl ketone (169) from the methanol adduct (168) was not adaptable for preparation of the gemdimethyl analogue (171). The photo addition of isopropanol to (83) gave an excellent yield of (170), but efforts to convert this into (171) were not encouraging.…”

Synthesis of a 4,5-unsaturated-3-keto sugar (methyl 2-O-benzoyl-4-deoxy-6-O-triphenylmethyl-α-D-glcero-hex-4-enopyranosid-3-ulose)

“…The unsaturated lactone 4 has also been prepared in our laboratory2 and hence the potential exists for carrying out conjugate addition reactions at carbons 1, 2, 3, and 4. Indeed many of these enones have been utilized in this way, having been proved of value for the syntheses of branched-chain (5, 6) and amino (7) sugars as well as for photoalkylation (8) and cycloaddition (9) reactions. The enone 5 is the only missing member of the series and for this reason we decided to attempt its synthesis.…”

“…Le processus implique sans aucun doute une tpimtrisation et le produit comporte un melange d u produit (5) desire (R = CPh,) et de son tpimere-2 (22). Ces enones peuvent subir facilement des dCcompositions catalysees par les bases; ceci implique que m@me si trois ttapes peuvent Etre effectuees, avec de bons rendements, a partir de la cttone (8) pour conduire au sulfonate ( l l b ) , l'elimination finale ne se produit qu'avec un rendement de 3 9 z en produit isole.…”