C-Glycosidation with Silylacetylenes to D-glucals

Carbon-Carbon Bond Forming Reactions by using Bistrifluoromethanesulfonimide

“…In general these reactions afford C-allylated glycosides with moder- [49][50][51][52][53] When tri-Oacetyl-D-glucal 37 was treated with allytrimethylsilane 28 in the presence of a catalytic amount of TFSI-H, the allylsubstituted dihydropyran 38 was obtained in 80% yield and as a 10/1 (a/b) diastereomeric mixture (Scheme 5). An example of alkynylation of tri-O-acetyl-D-glucal 37 54 was also achieved by BTMSA 1 in the presence of TFSI-H as a catalyst. Tri-O-acetyl-D-glucal 37 was transformed to compound 39 in a highly diastereoselective manner, as a single diastereomer with an a-axial orientated acetylenic substituent was obtained (36% yield) (Scheme 5).…”

Heteroconjugate Addition Strategy for the Synthesis of the (HIJ)K-Ring Fragment of Ciguatoxin

“…If this is true, it would make it possible to attach all the requisite carbon framework for the JKLM-ring segment in this step, because a building block of substituted propargyl ether representing LM-ring sector could be introduced to 1. 5 The orientation of this electrophilic moiety 1 is equatorial (the coupling constant is J 1, 1' = 9 Hz, namely, H-1 and H-1' is a trans relationship). It is expected that treatment of 1 with the lithium acetylide generated from substituted propargyl ethers with n-BuLi would provide 2 as a favorable adduct via bchelation as shown in Scheme 2.…”

“…The aldehyde C representing the LM-ring segment was synthesized from (S)-5-[(1S)-menthyloxy]-2(5H)-furanone. 5 However, the attempt at the addition of compound B to the aldehyde C afforded the undesired compounds D and E due to a similar acidity of the proton of the acetylene and the α-proton of the sulfonyl group.…”

Stereocontrolled synthesis and reactivity of sugar acetylenes

“…C-Glycosidation with silylacetylenes allows a wide variety of substituents on the other end of the acetylene, and the resulting alkynylated sugar derivatives are of great potential utility as starting materials for natural product synthesis in optically active form. 9 Examples with different substituents are listed in Table 1. [8][9][10] In the reaction, R has to be larger than Me to afford alkynylation in reasonably good yield.…”