Ring Opening of Epoxides and Aziridines with Sodium Azide using Oxone^®in Aqueous Acetonitrile: A Highly Regioselective Azidolysis Reaction

Abstract

A wide variety of epoxides and aziridines were converted to the corresponding b-azido alcohols and b-azido amines with sodium azide using Oxone ® in aqueous acetonitrile. The reactions were highly regioselective and efficient with excellent yields at room temperature under mild reaction conditions. Epoxides 2 and aziridines 3 are among the most useful synthetic intermediates in organic synthesis. Due to their three membered ring strain, they undergo facile, regioand stereoselective ring-opening reactions with various nucleophiles, yielding a broad range of valuable products. 4,5 Among these, the azidolysis of epoxides and aziridines enjoys a prominent position for the preparation of azido alcohols 6 and azido amines, 7 respectively. The vicinal azido alcohols are precursors of amino alcohols 8 which are well known as b-blockers and a common structural components in a vast group of natural products. 9 Further, they have also been utilized in carbohydrate chemistry 10 or in the chemistry of nucleosides. 11 The azido amines obtained upon ring opening are easily transformed to valuable vicinal diamines. 12 The classical reagents for azidohydrin synthesis are the combined use of TMSN 3 or NaN 3 and a Lewis acid or a transition metal complex. 13 In most of epoxide ring-opening reactions with NaN 3 under either alkaline or acidic conditions, suffer from high temperatures or long reaction times. In addition to these, side reactions, isomerizations, epimerization and rearrangements have also observed by the alkaline conditions of the reaction. It has been found that NaN 3 impregnated on a calcium cation exchange Y-type Zeolite induces the nucleophilic ring opening of epoxides in protic solvents affording azidohydrins. 14 Other reported reagents are tributyltinazide and dibutyltinazide, in DMF. 15 Use of phase transfer catalyst 16 has also been reported recently for the preparation of azidohydrins. Even though several procedures have appeared for the ring opening of epoxides, a limited number of methods have been available for the ring-opening reactions of aziridines. The most straightforward route to azido amines involves the regioselective ring opening of aziridines with TMSN 3 in the presence of a promoter. Tetrabutylammonium fluoride was found to promote the ring-opening reaction of aziridines with TMSN 3 . 12 Yeung and co-workers 17 reported the chromium complex mediated ring-opening reaction of aziridines with TMSN 3 . Transition metal-based complexes 18 were also used when N-benzoylaziridines were the substrates, but the rearrangement to oxazolines took place. As part of a programme aimed at the synthesis of epoxides and aziridines and their applications in organic synthesis, we have studied the ring opening reactions of these small heterocyclic compounds. 19 We recently found that potassium peroxymonosulfate, commonly sold as Oxone ® (2 KHSO 5 , KHSO 4 , K 2 SO 4 ) catalyze in an extraordinarily effective way the alcoholysis 20 of epoxides and aziridines in aqueous methanol. On this basis, we looked for an analog...

SO3H-Carbon derived from glycerol: An efficient and recyclable catalyst for smooth and regioselective azidolysis of oxiranes in water

“…Excellent yields of the desired β-azido alcohols are obtained with a reversal of regioselectivity indicating attack at the less substituted carbon of the aliphatic oxiranes (Entries 2-7, Table 2), while styrene oxide (Entry 1, Table 2), as an aryl oxirane formed the major product as 2-azido-2-phenylethanol, by the attack of azide nucleophile at the benzylic position, this is due to the formation of a stable benzyl carbocation during mechanism, is evidenced by electronic factors [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], whereas in the case of aliphatic oxiranes (Entries 2-7, Table 2), steric factors predominate over electronic factors, thereby facilitating attack at the less hindered carbon atom of the oxirane ring. Furthermore, oxiranes derived from cycloalkenes, such as 7-oxabicyclo [4.1.0]heptanes (Entry 2, Table 2), reacted smoothly in SN2 fashion to afford the corresponding azidohydrine; and the reaction was completely anti-sterioselective, thus resulting in trans isomer only.…”

“…Some heterogeneous catalysts, relying on the use of traditional solid acids such as amberlite IRA-400 supported azide [33]. Dowex resin grafted by poly ethylene glycol [34], oxone [35], sodium azide supported on Zeolite CaY [36], ammonium salt of a hetero poly acids [37], quaternized ammonium salt [38] and quaternized amino functionalized cross linked polyacrylamide [39] have been reported. Recently, hot water promoted azidolysis also reported [40].…”

Three‐Membered Heterocycles. Structure and Reactivity

“…To achieve virtually neutral conditions, trimethylsilyl azide can be used as the source of azide (Table 2.13, entry 1), along with catalytic amounts of tributylammonium fluoride (TBAF) to liberate the azide in situ [152]. Of course, sodium azide itself can be used as a reactant, with the addition being promoted efficiently by cerium trichloride heptahydrate [168], lithium perchlorate [169] or Oxone [170] (Scheme 2.25). Meso aziridines can be enantioselectively desymmetrized using a dimeric salen yttrium catalyst in near quantitative yield and excellent enantioselectivity [161].…”

An efficient catalyst-free ring opening of epoxides in peg-300: A versatile method for the synthesis of vicinal azidoalcohols

“…Azidation of epoxides as the most common synthetic route to 1,2-azidoalcohols are often performed in aqueous solutions under alkaline or acidic conditions [7] and several different methods have been devised in order to obtain the direct azidolysis of epoxides in the literature. The reaction of epoxides with triethylaluminium/HN 3 [8], NaN 3 /calcium cation exchange Y-type zeolite [9], tributyltin azide [10], dibutyltin diazide [11], NaN 3 /LiC1O 4 [12], TMSN 3 /Ti(O-i Pr) 4 [13], TMSN 3 /Cr(salen) [14], TMGA/Hf(OTf) 4 , Zr(OTf) 4 or Yb(OTf) 4 [15], diethylaluminium azide [16], NaN 3 /CAN [17], TMSN 3 /ȕ-Cyclodextrin [18], NaN 3 /PTC [19], NaN 3 /halohydrin dehalogenase [20], NaN 3 /CeCl 3 [21], NaN 3 /Oxone [22], NaN 3 /LiBF 4 [23], Azide exchange resin [24], NaN 3 /PVA (or PAA) [25], HN 3 /Co(salen) [ However, many of these methods involve the use of expensive and stoichiometric amounts of reagents or catalysts, suffer from poor regioselectivity, strongly acidic conditions and also require extended reaction times. Therefore, the development of a new and efficient protocol for this transformation under mild and more convenient conditions is still needed.…”