Remote acyl groups

Glycosylation with Donors Having Remote Acyl Groups. 558... 

Another factor, which can eliminate the effect of remote acyl groups, is the choice of a promoter. Thus, trimethylsilyl trifluoromethanesulfonate (TMSOTf)-promoted... 

Scheme 15 Stereoselective glycosylations by (a) a remote C-4 O-acyl group, (b) remote C-4, C-6 O-acyl groups, (c) a remote C-3 O-acyl group.

The 1,4,5-oxadiazepine 63 was transformed into 65 by a four-step reaction sequence (1) cleavage of both /-butoxycarbonyl (BOC) and the lactone, (2) acylation of the remote amino group with 2-(trimethylsilyl)ethyloxy-carbonyl chloride (TeocCl), (3) protection of the alcohol functionality with a silyl group, and (4) ester hydrolysis (Scheme 10) C1998AGE2995, 2001CEJ41>. 

An elegant deuterium labelling study of gold(I)-catalysed glycosidation of peracetyl glucopyranosyl orf/io-hexynylbenzoate revealed remote participation of the 4-0-acyl group (Scheme 85). ... 

Fig. 5 Possible dioxalynium ion intermediate by the remote participation of 3-0-acyl groups of mannosyl donors...

Nifantiev and co-workers investigated the effect of acyl groups at the 0-4 position of donors on the fucosylation stereochemistry fucosylations of acceptor 121 with fucosyl donors 118—120 having p-methoxybenzoyl, benzoyl, and p-nitrobenzoyl groups, respectively, at the 0-4 position were a-selective and thus disaccharides 123 (R = Bz, p/a = 1 3.5), 124 (R = p-NOjBz, p/a = 1 2), and 125 (R = p-OMeBz, p/a = 1 5) were obtained, respectively, with an excess of a-anomers (Table 8) [73]. The a-selectivity was ascribed to the remote participation of the 4-O-acyl groups and the computational work on the difference in the total energy... 

Van Leeuwen and coworkers [117] prepared a Xantphos-type ligand for application in RTILs (room-temperature ionic liquids) bearing remote imidazolium groups (Scheme 2.34). In the first step, the xanthene-based backbone was functionalized by Friedel-Crafts acylation using 5-bromovaleraldehyde. After reduction of the keto groups, two POP units were introduced. Final incorporation of methyl-imidazolium groups yielded the final ligand. In the first runs of the rhodium-catalyzed hydroformylation of 1-octene in [BMlM][PFg], a diminished activity was noted, obviously due to incomplete conversion of the precatalyst into... 

First, another research group has directly demonstrated a possibility of the remote participation of an acyl group at equatorial 0-3 by conversion of mannosyl donor 13 into 1,3-bicycle 14 (Scheme 5.5c) [12]. Acyl groups at equatorial O-3 in glucosyl donors also display an evident stereodirecting effect despite the... 

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