Efficient route to 2H-1,3-oxazines through ring expansion of isoxazoles by rhodium carbenoids

Manning, James R.; Davies, Huw M. L.

doi:10.1016/j.tet.2008.03.010

Cited by 76 publications

(22 citation statements)

References 25 publications

(11 reference statements)

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“…The structure of pyridine 15b has been unambiguously determined by Xray crystallography. 9 (5) In summary, an efficient one-pot procedure for the synthesis of highly functionalized pyridines and 1,4-dihydropyridines has been developed. The reaction proceeds via an initial carbenoid induced ring expansion of isoxazoles followed by a rearrangement/ tautomerization/oxidation sequence.…”

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confidence: 99%

One-Pot Synthesis of Highly Functionalized Pyridines via a Rhodium Carbenoid Induced Ring Expansion of Isoxazoles

2008

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One-Pot Synthesis of Highly Functionalized Pyridines via a Rhodium Carbenoid Induced Ring Expansion of Isoxazoles

2008

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“…To start with, we reacted 4-phenyl-substituted isoxazole 1a and phenyldiazoacetate 2a under the reaction conditions used in [ 4 ] (catalyst: 1–3 mol % of Rh 2 (OAc) 4 , solvent: CH 2 Cl 2 or ClCH 2 CH 2 Cl, 40 or 84 °C) ( Scheme 3 ). Unexpectedly, attempts to prepare oxazine 3a under these conditions were unsuccessful ( Scheme 3 ) and isoxazole 1a was completely recovered.…”

Section: Resultsmentioning

confidence: 99%

“…However, reactions of isoxazoles with diazo compounds have scarcely been studied [ 1 – 5 ]. In 2008 Davies and Manning [ 4 – 5 ] discovered the Rh-catalyzed reaction of diazo esters with 3,5-dialkylisoxazoles, benzo[ d ]isoxazole and 3-chlorobenzo[ d ]isothiazole leading to the corresponding 2 H -1,3-oxazines, 2 H -benzo[ e ][1,3]oxazine and 2 H -benzo[ e ][1,3]thiazine.…”

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confidence: 99%

Isoxazolium N-ylides and 1-oxa-5-azahexa-1,3,5-trienes on the way from isoxazoles to 2H-1,3-oxazines

Khlebnikov¹,

Новиков²,

Gorbunova³

et al. 2014

Beilstein J. Org. Chem.

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SummaryTheoretical and experimental studies of the reaction of isoxazoles with diazo compounds show that the formation of 2H-1,3-oxazines proceeds via the formation of (3Z)-1-oxa-5-azahexa-1,3,5-trienes which undergo a 6π-cyclization. The stationary points corresponding to the probable reaction intermediates, isoxazolium N-ylides, were located by DFT calculations at the B3LYP/6-31G(d) level only for derivatives without a substituent in position 3 of the isoxazole ring. These isoxazolium N-ylides are thermodynamically and kinetically very unstable. According to the calculations and experimental results 2H-1,3-oxazines are usually more thermodynamically stable than the corresponding open-chain isomers, (3Z)-1-oxa-5-azahexa-1,3,5-trienes. The exception are oxaazahexatrienes derived from 5-alkoxyisoxazoles, which are thermodynamically more stable than the corresponding 2H-1,3-oxazines. Therefore, the reaction of diazo esters with 5-alkoxyisoxazoles is a good approach to 1,4-di(alkoxycarbonyl)-2-azabuta-1,3-dienes. The reaction conditions for the preparation of aryl- and halogen-substituted 2H-1,3-oxazines and 1,4-di(alkoxycarbonyl)-2-azabuta-1,3-dienes from isoxazoles were investigated.

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“…Aryl-, benzoyl-, and tosyl-substituted -diazoacetic esters 2c-f as well as 3-diazopentane-2,4-dione (2j) were decomposed by both Rh 2 (OAc) 4 and Rh 2 (Piv) 4 without any conversion of oxadiazole 1a (Table 1, entries [3][4][5][6][7][8][9][10][11][12][13][14][15][16]12). The reason for the failure is probably the low nucleophilicity of the oxadiazole.…”

Section: Paper Synthesismentioning

confidence: 99%

An Efficient Synthesis of Functionalized 2H-1,3,5-Oxadiazines via Metal-Carbenoid-Induced 1,2,4-Oxadiazole Ring Cleavage

et al. 2020

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A high-yielding method for the synthesis of 2H-1,3,5-oxadiazines by rhodium(II)- or copper(II)-catalyzed reaction of 1,2,4-oxadiazoles with α-diazo esters has been developed. The reaction proceeds via attack of the metallocarbenoid on the oxadiazole N2 atom followed by ring opening/1,6-electrocyclization and enables the introduction of alkyl, aryl, oxy, and amino substituents into the 6-position and electron-withdrawing groups into the 2-position of 1,3,5-oxadiazine. The N2-attack and the N4-attack of the carbenoid cause different oxadiazole ring openings, which are controlled by the substitution at C5. The presence of a substituent at this position is a prerequisite for the N2-attack to occur, leading to the formation of 1,3,5-oxadiazines.

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Efficient route to 2H-1,3-oxazines through ring expansion of isoxazoles by rhodium carbenoids

Cited by 76 publications

References 25 publications

One-Pot Synthesis of Highly Functionalized Pyridines via a Rhodium Carbenoid Induced Ring Expansion of Isoxazoles

One-Pot Synthesis of Highly Functionalized Pyridines via a Rhodium Carbenoid Induced Ring Expansion of Isoxazoles

Isoxazolium N-ylides and 1-oxa-5-azahexa-1,3,5-trienes on the way from isoxazoles to 2H-1,3-oxazines

An Efficient Synthesis of Functionalized 2H-1,3,5-Oxadiazines via Metal-Carbenoid-Induced 1,2,4-Oxadiazole Ring Cleavage

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