Diastereoselectivity in the Reaction of N‐Glycosyl‐nitrones: 1,3‐Dipolar Cycloaddition and Addition of Phosphite Anion

Abstract

The direction of approach of dibenzyl phosphite on the one hand and of dipolarophiles on the other hand to the spironitrone 7 was examined. The nitrone 7 was prepared from the lactone 3. The nucleophilic addition of dibenzyl phosphite gave 8 as a single adduct (86%). Its structure was established by X-ray analysis. From the cycloaddition of methyl methacrylate, the products 9a, 9b, l l a , and l l b (83:2:7.5:7.5, 81 %) were isolated. The structure of the main adduct 9a was established by an X-ray analysis of a derivative of it, and the structures of the other adducts were deduced from their NMR spectra. The cycloaddition of 7 and methyl acrylate gave the adducts 10a, lob, 12a, 13a, 13b, and 14a (27:10:54:1:2:6,87%). The structures of these compounds were deduced from their NMR spectra. The results are discussed in relation to prior hypothesis.1. Introduction. -The nucleophilic addition of dialkyl phosphite anions to (2)-Calkyl-N-(2,3 : 5,6-di-0 -isopropylidene-cc -D-mannofuran0syl)nitrones 1 gives the (1 S ) -Nglycosyl-N-hydroxyaminophosphonates 2 with a diastereoselectivity of about 90 % [ 11 (Scheme I ) . A high diastereoselectivity had been predicted, based on the analogy between a LUMO-controlled 1,3-dipolar cycloaddition of N-glycosyl-nitrones and the addition of nucleophiles to it [ 11.

Synthesis of Amino‐L‐Lyxose Phosphonates as Fucosyl‐Phosphate Mimics

“…Scheme 2. The N-OH group is generally reduced by hydrogenolysis over Pd/C, [15,18] and even better in the presence of aqueous HCl. [16,17] We have verified that this reduction also occurred by hydrogenolysis over Raney-nickel [20] but not over 5 % Pd/ C alone. O,N-Bis-deprotection of 6a,b was finally carried out by hydrogenolysis with 5 % Pd/C in EtOH and aqueous 1  HCl to give in one step the pyrrolidine-phosphonates 7a,b as hydrochlorides.…”

“…Addition of alkyl phosphites to nitrones has been carried out by Lewis acid catalysis, [15,16] with its anion [17,18] or in the absence of solvents. [19] By using this last condition (Scheme 2), the reaction of nitrone 4 with dialkyl esters 5a-c at 40°C gave the N-hydroxy-phosphonates 6a,b in quantitative yields whereas the bulky dibenzyl derivative 6c was only obtained in a moderate yield (47 %).…”

Asymmetric 1,3-Dipolar Cycloaddition Reactions

“…The first application of an optically active cyclic nitrone in 1,3-DC reactions was reported by Vasella et al in 1985 51 and during the last 5 years a number of successful reactions of optically active cyclic nitrones have been published. [52][53][54][55][56][57][58][59][60][61][62][63][64][65][66] Brandi et al have studied the application of the L-tartaric acid derived nitrones 42a-d. [55][56][57]63,65,66 Nitrone 42e shows a high degree of chiral discrimination in the 1,3-DC reaction with methylenecyclopropane at rt, leading to one regioisomer in a yield of 75% with a de of 82%.…”

Carbohydrate-auxiliary assisted preparation of enantiopure 1,2-oxazine derivatives and aminopolyols

“…2:1 ratio, in the case of lithiated benzyloxyallene a significant switch of the selectivity to an approximate 1:2 ratio was observed. According to the model proposed in the literature [ 7 , 18 , 20 ] for the addition of nucleophiles, the stereochemical course is governed by a competition of steric and electronic effects. As presented in Fig.…”