Dichotomy of 1,3-dipolar cycloreversions in a tetrasubstituted 2,5-dihydro-1,3,4-thiadiazole

Langhals, Elke; Huisgen, Rolf

doi:10.1002/hc.20263

Cited by 2 publications

References 16 publications

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Twofold Extrusion Reactions

Guziec

2012

Organic Reactions

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Twofold extrusion reactions are chemical transformations in which two small inorganic molecules or atoms connecting carbon or nitrogen atoms are lost, generating the corresponding carbon‐carbon or carbon‐nitrogen double bonds. These reactions are particularly useful for the preparation of sterically hindered alkenes and imines. The inorganic species liberated in twofold extrusion reactions can be molecular nitrogen, sulfur, selenium, tellurium, sulfur dioxide, sulfur monoxide, carbon dioxide or carbon monoxide. The most common precursors for twofold extrusion reactions are 1,3,4‐thiadiazolines, which thermally extrude molecular nitrogen affording thiiranes. These thiiranes can be readily desulfurized to afford the corresponding alkenes using tertiary phosphines. The corresponding 1,3,4‐selenadiazolines thermally extrude both molecular nitrogen and atomic selenium directly affording alkenes. Alkenes can also be prepared by formal extrusions of molecular nitrogen plus sulfur dioxide or sulfur monoxide. Extremely sterically hindered imines can be prepared by extrusions of molecular nitrogen and sulfur or selenium from in situ generated heterocyclic precursors. Other less common twofold extrusion reactions are also reported. The detailed preparations of the required precursors for the twofold extrusion reactions as well as the mechanisms of these extrusion processes are discussed in this chapter. The utility of twofold extrusion reactions in the preparations of ‘molecular rotors’ and other extremely sterically hindered alkenes is presented. The steric limitations of the twofold extrusion reactions are discussed along with comparisons of these reactions with other alkene‐ and imine‐forming synthetic methods. The Tabular Survey covers material through the end of 2009.

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Twofold Extrusion Reactions

Guziec

2012

Organic Reactions

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Reactions of Methyl Diazoacetate with (E)‐ and (Z)‐1,2‐Bis(trifluoromethyl)ethene‐1,2‐dicarbonitrile: Novel and Unanticipated Pathways

Huisgen

Mlostoń

Pöchlauer

et al. 2007

Helvetica Chimica Acta

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Dedicated to Mordecai Rubin, Technion, Haifa, on the occasion of his 80th birthdayThe cycloadditions of methyl diazoacetate to 2,3-bis(trifluoromethyl)fumaronitrile ((E)-BTE) and 2,3-bis(trifluoromethyl)maleonitrile ((Z)-BTE) furnish the 4,5-dihydro-1H-pyrazoles 13. The retention of dipolarophile configuration proceeds for (E)-BTE with > 99.93% and for (Z)-BTE with > 99.8% (CDCl 3 , 258), suggesting concertedness. Base catalysis (1,4-diazabicyclo[2.2.2]octane (DABCO), proton sponge) converts the cycloadducts, trans-13 and cis-13, to a 94 : 6 equilibrium mixture (CDCl 3 , r.t.); the first step is N-deprotonation, since reaction with methyl fluorosulfonate affords the 4,5-dihydro-1-methyl-1H-pyrazoles. Competing with the cis/trans isomerization of 13 is the formation of a bis(dehydrofluoro) dimer (two diastereoisomers), 2 C 9 H 4 F 6 N 4 O 2 (13) ! C 18 H 6 F 10 N 8 O 4 (22) + 2 HF, the structure of which was elucidated by IR, 19 F-NMR, and 13 C-NMR spectroscopy. The reaction slows when DABCO is bound by HF, but F À as base keeps the conversion to 22 going and binds HF. The diazo group in 22 suggests a common intermediate for cis/trans isomerization of 13 and conversion to 22: reversible ring opening of N-deprotonated 13 provides 18, a derivative of methyl diazoacetate with a carban-A C H T U N G T R E N N U N G ionic substituent. Mechanistic comparison with the reaction of diazomethane and dimethyl 2,3-dicyanofumarate, a related tetra-acceptor-ethylene, brings to light unanticipated divergencies.

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Dichotomy of 1,3-dipolar cycloreversions in a tetrasubstituted 2,5-dihydro-1,3,4-thiadiazole

Abstract: The cycloaddition of diphenyldiazomethane (8) to 16 thioketones at 40• C which furnishes tetrasubstituted 2,5-dihydro-1,3,4-

Cited by 2 publications

References 16 publications

Twofold Extrusion Reactions

Twofold Extrusion Reactions

Reactions of Methyl Diazoacetate with (E)‐ and (Z)‐1,2‐Bis(trifluoromethyl)ethene‐1,2‐dicarbonitrile: Novel and Unanticipated Pathways

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