Base catalyzed cyclization of N-aryl and N-alkyl-O-propargyl carbamates to 4-alkylidene-2-oxazolidinones

Ramesh, Ramapanicker; Chandrasekaran, Yogesh; Rajendran, Megha; Chandrasekaran, Srinivasan

doi:10.1016/j.tet.2007.06.066

Cited by 37 publications

(22 citation statements)

References 17 publications

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“…With the phenyl-substituted alkynes 8 b and 8 c, the migration was followed by cyclisation of the resulting carbamate anion 15 Li onto the triple bond [27] to yield the benzylidene oxazolidinones (E)-and (Z)-16 (Table 1, entries 6-10) in a ratio dependent upon the base used in the cyclisation. As with 7 a, primary O-propargylcarbamate 8 a, on treatment with base, produced products of attack directly on the carbamate C=O group.…”

Section: Resultsmentioning

confidence: 99%

Lithium Choreography: Intramolecular Arylations of Carbamate‐Stabilised Carbanions and Their Mechanisms Probed by In Situ IR Spectroscopy and DFT Calculations

Fournier

Nichols

Vincent

et al. 2012

Chemistry A European J

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Deprotonation of O-allyl, O-propargyl or O-benzyl carbamates in the presence of a lithium counterion leads to carbamate-stabilised organolithium compounds that may be quenched with electrophiles. We now report that when the allylic, propargylic or benzylic carbamate bears an N-aryl substituent, an aryl migration takes place, leading to stereochemical inversion and C-arylation of the carbamate α to oxygen. The aryl migration is an intramolecular S(N) Ar reaction, despite the lack of anion-stabilising aryl substituents. Our in situ IR studies reveal a number of intermediates along the rearrangement pathway, including a "pre-lithiation complex," the deprotonated carbamate, the rearranged anion, and the final arylated carbamate. No evidence was obtained for a dearomatised intermediate during the aryl migration. DFT calculations predict that during the reaction the solvated Li cation moves from the carbanion centre, thus freeing its lone pair for nucleophilic attack on the remote phenyl ring. This charge separation leads to several alternative conformations. The one having Li(+) bound to the carbamate oxygen gives rise to the lowest-energy transition structure, and also leads to inversion of the configuration. In agreement with the IR studies, the DFT calculations fail to locate a dearomatised intermediate.

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Section: Resultsmentioning

confidence: 99%

Lithium Choreography: Intramolecular Arylations of Carbamate‐Stabilised Carbanions and Their Mechanisms Probed by In Situ IR Spectroscopy and DFT Calculations

Fournier

Nichols

Vincent

et al. 2012

Chemistry A European J

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“…Because of the continuous generation of the requisite base at low concentration, basepromoted ionic cyclization [5] of 2 is avoided (Scheme S1). Ther eaction begins with the anodic oxidation of tetraarylhydrazine 1 (E p/2 = 0.68 Vv s. saturated calomel electrode,S CE), which produces as table radical-cation intermediate A.M eanwhile,h ydroxide is generated from the reduction of H 2 Oa tt he cathode and it deprotonates 2 to afford the anion B,the oxidation potential of which is significantly lower than that of 2 (E p/2 = 1.76 Vfor 2,0 .66 Vf or B,v s. SCE).…”

Section: Angewandte Chemiementioning

confidence: 99%

“…[1] Despite the recent resurgence of interests in organic radical chemistry,r adical C À Nb ond formation reactions remain underdeveloped. [3] In comparison, there have only been af ew studies on the cyclization of N-centered radicals with alkynes, [4] probably due to the lack of versatile radical initiation methods and the competing ionic cyclization reaction [5] when using aN ÀH-based radical precursor.O nt he other hand, there is also al ack of CÀNb ond-forming cyclization reactions employing C-centered radicals, [6] which show as trong preference for reaction with the carbon instead of the nitrogen in N-containing p-systems. [3] In comparison, there have only been af ew studies on the cyclization of N-centered radicals with alkynes, [4] probably due to the lack of versatile radical initiation methods and the competing ionic cyclization reaction [5] when using aN ÀH-based radical precursor.O nt he other hand, there is also al ack of CÀNb ond-forming cyclization reactions employing C-centered radicals, [6] which show as trong preference for reaction with the carbon instead of the nitrogen in N-containing p-systems.…”

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confidence: 99%

Electrochemical Synthesis of Imidazo‐Fused N‐Heteroaromatic Compounds through a C−N Bond‐Forming Radical Cascade

et al. 2018

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“…The base-promoted cyclization of Opropargyl carbamates has long been established. 5 The intermolecular hydroamination of O-propargyl carbamates in the presence of a transition metal, such as Cu 2+ or Au + salt, has also been reported. 6 Baba and co-workers reported that the addition of allyltin reagents to a,b-unsaturated aldehyde, followed by treatment with isocyanates, gave 2-oxazolidinones in one-pot reactions.…”

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confidence: 99%

One-Pot, Three-Component Synthesis of Chiral 4-Alkylidene-2-oxazolidinones

Kojima¹,

Nishijima²,

Tanaka³

2009

Synlett

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A one-pot convenient access to chiral 2-oxazolidinones is described. Diethylzinc-mediated asymmetric alkynylation of aldehydes with propiolates in the presence of b-sulfonamide alcohol as the chiral ligand, followed by treatment with isocyanates, yielded chiral 4-alkylidene-2-oxazolidinones.Avid interest in modern organic chemistry has been directed toward the development of simple and convenient ways to access useful heterocyclic compounds under mild and environmentally friendly conditions. Multicomponent reactions (MCR) have recently emerged as a valuable tool for the preparation of chemical libraries of druglike heterocyclic compounds. 1 2-Oxazolidinones play prominent roles in daily life. They are widely used in pharmaceutical manufacturing, 2 agriculture, and industry, and as chiral auxiliaries in organic synthesis. 3 Among the many methods for the syntheses of 2-oxazolidinones, 4 the 5-exo cyclization of O-propargyl or O-allyl carbamates is one of the most attractive methods because it enables easy access to various substituted 2-oxazolidinones. The base-promoted cyclization of Opropargyl carbamates has long been established. 5 The intermolecular hydroamination of O-propargyl carbamates in the presence of a transition metal, such as Cu 2+ or Au + salt, has also been reported. 6 Baba and co-workers reported that the addition of allyltin reagents to a,b-unsaturated aldehyde, followed by treatment with isocyanates, gave 2-oxazolidinones in one-pot reactions. 7 Herein, we report the one-pot, three-component synthesis of chiral 4-alkylidene-2-oxazolidinones with aldehydes, propiolates, and isocyanates.Although the asymmetric alkynylation of carbonyl compounds by zinc acetylides is a well-known method for the synthesis of chiral propargyl alcohol derivatives, 8 the resulting zinc alkoxides have been scarcely used for further transformation as most zinc-oxygen bonds are hydrolyzed to propargyl alcohols despite their sufficient nucleophilicity. We devised a one-pot synthesis of chiral 2-oxazolidinones, which involved asymmetric alkynylation of aldehydes with propiolates, followed by treatment with isocyanates. Initial screening of the reaction conditions demonstrated that the conditions developed by Wang's group 9 gave the best results for our purpose.Diethylzinc-mediated (3.0 equiv) asymmetric alkynylation of cyclohexanecarbaldehyde (1.0 equiv) with ethyl propiolate (3.0 equiv) in the presence of Ti(Oi-Pr) 4 (30 mol%) and 1,2-dimethoxyethane (DME, 1.0 equiv) using b-sulfonamide alcohol (30 mol%) as the chiral ligand in toluene at room temperature, followed by treatment with tosyl isocyanate (3.2 equiv), afforded (R,E)-4-alkylidene-3-tosyloxazolidin-2-one 1a in 77% yield with good enantioselectivity 10 and complete E-stereoselectivity 11 (Table 1, entry 1). 12,13 To demonstrate the generality of this method, we examined the scope and limitations of the present one-pot synthesis (Table 1). The reaction with methyl or tert-butyl propiolates in place of ethyl propiolate also proceeded under the same conditions and ...

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Base catalyzed cyclization of N-aryl and N-alkyl-O-propargyl carbamates to 4-alkylidene-2-oxazolidinones

Cited by 37 publications

References 17 publications

Lithium Choreography: Intramolecular Arylations of Carbamate‐Stabilised Carbanions and Their Mechanisms Probed by In Situ IR Spectroscopy and DFT Calculations

Lithium Choreography: Intramolecular Arylations of Carbamate‐Stabilised Carbanions and Their Mechanisms Probed by In Situ IR Spectroscopy and DFT Calculations

Electrochemical Synthesis of Imidazo‐Fused N‐Heteroaromatic Compounds through a C−N Bond‐Forming Radical Cascade

One-Pot, Three-Component Synthesis of Chiral 4-Alkylidene-2-oxazolidinones

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Base catalyzed cyclization of N-aryl and N-alkyl-O-propargyl carbamates to 4-alkylidene-2-oxazolidinones

Cited by 37 publications

References 17 publications

Lithium Choreography: Intramolecular Arylations of Carbamate‐Stabilised Carbanions and Their Mechanisms Probed by In Situ IR Spectroscopy and DFT Calculations

Lithium Choreography: Intramolecular Arylations of Carbamate‐Stabilised Carbanions and Their Mechanisms Probed by In Situ IR Spectroscopy and DFT Calculations

Electrochemical Synthesis of Imidazo‐Fused N‐Heteroaromatic Compounds through a C−N Bond‐Forming Radical Cascade

One-Pot, Three-Component Synthesis of Chiral 4-Alkylidene-2-oxazolidin­ones

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One-Pot, Three-Component Synthesis of Chiral 4-Alkylidene-2-oxazolidinones