Fluorination of 2-hydroxy-hexopyranosides by DAST: towards formyl C-glycofuranosides from equatorial-2-OH methyl hexopyranosides

Rearrangements accompanying fluorination of 2-amino alcohols and 1,2-diols with Deoxo-Fluor™

“…Generally, DeoxoFluor TM and DAST readily convert alcohols to alkyl fluorides, aldehydes/ketones to gem-difluorides, and carboxylic acids to the corresponding trifluoromethyl derivatives. However, in some cases, Deoxo-Fluor TM and DAST can initiate the formation of rearranged products, for example, a-fluoro-b-amino acids were prepared from b-hydroxy-aamino acids mediated by DAST [5], the neighboring group participated in the rearrangement of the indole nucleus [6], the bicyclic epoxy alcohols rearranged to a ring expanded fluoride via the C-C bond cleavage of an oxirane ring with DAST [7], pyranosides rearranged to ring-contracted derivatives [8], and a stereoselective rearrangement of azabicyclo[2.1.1]hexane was initiated by Deoxo-Fluor TM [9].…”

Efficient synthesis of multifunctional furanoid C-glycoamino acid precursors

“…This reaction is a new example of the DAST-mediated rearrangement previously observed in other equatorial-2-OH glycopyranosides. 26 The H(1)/ F coupling constant values observed for 10a and 10b (J = 68 Hz for 10a, and J = 63 Hz for 10b) are in the range observed 38 for ring-contracted products (J = 63-68 Hz). Assignment of configuration to these epimers was made on the basis of the H(2)/F coupling constant value (J = 11.5 Hz for 10a, J = 3.1 Hz for 10b, suggesting 39 the H(2)/F gauche relationship in both cases, as an anti one would lead to a J value of $20 Hz), and the C(2)/F coupling constant value, lower for 10a (J = 11.5 Hz) than for 10b (J = 32.7 Hz), in agreement 39 with the F/ring O gauche and anti relationships, respectively.…”

“…[15][16][17][18][19][20] Several types of cyclic molecules (cyclic peptides, calix [4]arenes, cholic acid, and carbohydrates, among others) [21][22][23][24] have been used as templates for multivalent assembly, and it seems to be that the topology of multivalent peptides can be controlled by the defined spatial orientation of the functionalities on the rigid scaffold core. 25 On the basis of our previous experience with formyl nitro-and azido-C-glycofuranosides, [26][27][28] we recently started a project based on exploiting the potential of these readily available compounds for the synthesis of hydrolytically stable glycoamino acids (GAAs). GAAs, [29][30][31] which are carbohydrates bearing both an amino group and a carboxyl group, are ideal building blocks 32 to generate peptidomimetics because of their rigidity and multifunctionality.…”

Stereospecific mono- and difluorination of the C7-bridge of norbornenes

“…The cases where DAST mediated fluorinations result in exclusive retention of configuration involve neighboring group participation [6]. This anchimeric assistance is generally observed with nucleophilic neighboring groups, like sulfur (R-S-R) [32], oxygen (-OMe) [33], nitrogen (-N 3 ) [33] and bromine (R-Br) [34], which are able to displace the OSF 2 NEt 2 (10) leaving group. In addition, in one case, p-electrons of an adjacent double bond are also in position to displace this group [35].…”