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Cyclopropanated glycals

Nucleosides based upon monocyclic, fused and spirocyclic oxepines have been synthesised via nitrone cycloaddition reactions <07JOC7427>, while oxepine nucleic acids were synthesised from the ring expansion of cyclopropanated glycals <07JACS8259>. [Pg.438]

Scheme 15. Carbohydrate-type oxepine via cyclopropanation of a glycal. Scheme 15. Carbohydrate-type oxepine via cyclopropanation of a glycal.
In the previous section, the cyclopropanation of a glycal to form a bicyclic intermediate was followed by a ring-expansion reaction en route to each oxepine. Presented here are routes that afford oxepines either by ring-closing metathesis (RCM) reactions or by cycloisomerization of terminal alkynes. [Pg.143]

Scheme 41 Synthesis a furanose-fused butyrolactone from a glycal-derived cyclopropane... Scheme 41 Synthesis a furanose-fused butyrolactone from a glycal-derived cyclopropane...
More recently, another methodology for sugar-fused butyrolactones employing glycal-derived cyclopropane precursors has been described by Chandrasekaran and co-workers (Scheme 44) [215]. In this case, hexofuranose- or hexopyranose-1,2-fused were cyclopropanated into compounds of type 181. After saponification with... [Pg.52]

The cycloaddition of carbenes to glycals is an effective method for the formation of cyclopropanated carbohydrates with high stereoselectivity,60... [Pg.66]

K. J. Henry and B. Fraser-Reid, Cyclopropanation of glycals applications to the synthesis of 2-deoxy-2-vinylglycosides, Tetrahedron Lett., 36 (1995) 8901-8904. [Pg.109]

Studies involving cyclopropanation of glycals with ethyl diazoacetate in the presence of catalytic rhodium acetate or copper powder have also been reported <1995TL8901, 1996TL2533, 20010L2563>. [Pg.405]

Murali, R, Ramana, C V, Nagarajan, N, Synthesis of 1,2-cyclopropanated sugars from glycals, J. Chem. Soc. Chem. Common., 217—218, 1995. [Pg.495]

The synthesis of the required compound 61 commenced with the D-glucal derivative 57 (Scheme 11.16), the cyclopropanation of which gave the (3-derivative 58 as the major compound [63]. Opening the latter gave the intermediate mercurio derivative 59, which was reduced to 60. Final mesylation at the anomeric center followed by spontaneous elimination yielded the branched-glycal 61. This compound was in turn debenzylated [62]. [Pg.514]

Complementing cyclopropanation reactions, the dichlorocyclopropanation of glycals has also been used as a means to introduce methyl groups at sugar C2 positions. An excellent illustration of this strategy was reported in connection with a synthesis of the C29 to C51 fragment of altohyrtin A [64]. [Pg.515]

Other complementary methodologies include the preparation of substituted cyclopropanes from glycals using rhodium acetate carbenoid additions [65,66]. Additionally, acid catalyzed cyclopropane opening reactions in alcoholic solutions afford the 2-C-branched-glycosides. These combined reactions were used to prepare a key intermediate in marine diterpene norrisolide synthesis from D-mannose [67]. [Pg.515]

Timmers, C M, Leeuwenburgh, M A, Verheijen, J C, van der Marel, G A, van Boom, J H, Rhodium(Il) catalyzed asymmetric cyclopropanation of glycals with ethyl diazoacetate, Tetrahedron Asymmetry, 7, 49-52, 1996. [Pg.574]

Compound 110 (obtained by reaction of D-glucal with propargylic alcohol) was subjected to cyclization with Co2(CO)g, which led to a fused tricyclic derivative 111 (O Scheme 48) [97]. [2+2] Cycloaddition of carbenes to glycals is an efficient route leading to cyclopropanated sugars with high stereoselectivity [1]. Such cyclopropanes can be transformed into a number... [Pg.370]

It has been reported that the glycal 348 undergoes cyclopropanation to give 349 or 350 as the major products, depending on the choice of reagent [99]. Treatment of 348 with ethyl diazoacetate in the presence of rhodium diacetate gave a 59% yield... [Pg.110]

Scheme 15 Spiro anomeric cyclopropanes from dichloro-exo-glycals. Scheme 15 Spiro anomeric cyclopropanes from dichloro-exo-glycals.
Otherwise, the leaving group may be in the homoallylic situation either in the glycal itself or on a branch carbon atom in both situations the double-bond electrons of the glycal bond to the homoallylic carbon atom to give products with cyclopropane rings fused to furanoid or pyranoid rings, respectively. In this way compounds 76 [105] and 77 [106] are converted to cyclopropa-furanoid and -pyranoid nucleosides (Schemes 25 and 26, respectively). [Pg.172]

Glycals have been extensively used for the synthesis of a wide range of carbohydrate derivatives such as C-, S-/ and N-glycosides, cyclopropanated carbohydrates, and natural products. In particular, the Perrier and the azidonitration reactions, together with Danishefsky s glycal methodology (through epoxides), represent the most widely exploited applications. [Pg.253]


See other pages where Cyclopropanated glycals is mentioned: [Pg.167]    [Pg.221]    [Pg.267]    [Pg.268]    [Pg.167]    [Pg.221]    [Pg.267]    [Pg.268]    [Pg.405]    [Pg.436]    [Pg.11]    [Pg.127]    [Pg.139]    [Pg.141]    [Pg.51]    [Pg.52]    [Pg.514]    [Pg.514]    [Pg.515]    [Pg.318]    [Pg.322]    [Pg.332]    [Pg.675]    [Pg.112]    [Pg.500]    [Pg.500]    [Pg.501]    [Pg.1046]    [Pg.135]    [Pg.135]   
See also in sourсe #XX -- [ Pg.267 ]




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