Benzylo×y(4-substituted benzylo×y)carbenes. Generation from o×adiazolines and fragmentation to radical pairs in solution

Merkley, Nadine; Warkentin, John

doi:10.1139/cjc-78-7-942

Cited by 8 publications

(6 citation statements)

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“…The thermal treatment of the titanium analogues (TTP)Ti[OC(Me) 2 C(Me) 2 O] ( 5 ) and (TTP)Ti[OC(Me)(Ph)C(Me)(Ph)O] ( 6 ) under air in C 6 D 6 resulted in the formation of (TTP)TiO and the corresponding ketones as observed for hafnium. Under N 2 , the titanium pinacolate was converted initially to a paramagnetic species with δ 2.50 and 2.40 ppm resonances, accompanied by the production of acetone in 43−48% yield (eq 5) . One paramagnetic species could be only partially trapped by a large excess of pyridine to form a bis-pyridine adduct, (TTP)Ti(py) 2 .…”

Section: Resultsmentioning

confidence: 99%

Synthesis, Characterization, and Reactivity of Group 4 Metalloporphyrin Diolate Complexes

Woo

2002

Organometallics

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A number of group 4 metalloporphyrin diolate complexes were synthesized via various approaches. For example, treatment of imido complex (TTP)Hf NAriPr with diols resulted in formation of the corresponding diolato complexes (TTP)Hf[OCR1R2CR1R2O] (R1 = R2 = Me, 1; R1 = Me, R2 = Ph, 2; R1 = R2 = Ph, 3). Treatment of (TTP)TiNiPr with diols generated (TTP)Ti[OCR1R2CR1R2O] (R1 = R2 = Me, 5; R1 = Me, R2 = Ph, 6; R1 = H, R2 = Ph, 7; R1 = H, R2= p-tolyl, 8). Alternatively hafnium and titanium pinacolates 1 and 5 were prepared through metathetical reactions of (TTP)MCl2 (M = Hf, Ti) with disodium pinacolate. The substitution chemistry of hafnium complexes correlated well with the basicity of the diolato ligands. Complexes 1−6 underwent oxidative cleavage reaction, producing carbonyl compounds and oxometalloporphyrin species. For less substituted diolates 7 and 8, an array of products including the enediolate complexes (TTP)Ti[OC(Ar)C(Ar)O] (Ar = Ph, 9; Ar = p-tolyl, 10) was observed. The possible cleavage reaction pathways are discussed.

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Section: Resultsmentioning

confidence: 99%

Synthesis, Characterization, and Reactivity of Group 4 Metalloporphyrin Diolate Complexes

Woo

2002

Organometallics

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“…Most importantly, Merkley and Warkentin found that in the homolytic fragmentations of PhCH 2 OCOCH 2 Ar at 110 °C, the competitive formation of ArCH 2 · vs PhCH 2 · was 11.4/1 (Ar = p -nitrobenzyl), 3.0/1 (Ar = p -trifluoromethylbenzyl), and 0.94/1 ( p -tolyl) . Electron-withdrawing groups dominate homolytic carbene fragmentation.…”

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confidence: 99%

A Duality of Mechanisms for the Fragmentation of Substituted Benzyloxychlorocarbenes

Moss

Sauers

2002

J. Am. Chem. Soc.

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Substituted benzyloxychlorocarbenes (X-PhCH2OCCl) were generated photochemically at 25 degrees C in dichloroethane from appropriate diazirine precursors. Fragmentations of the carbenes produced were determined by laser flash photolysis. The data (X, kfrag in s-1) were: p-Me, 2.6 x 105; p-Ph, 8.3 x 104; H, 6.0 x 104; p-Cl, 5.2 x 104; m-Cl, 1.3 x 105; p-F3C, 2.1 x 106; p-O2N, 6.3 x 106. A Hammett correlation of log kfrag versus sigma+ was parabolic. The curvature was taken to imply the gradual change of the fragmentation mechanism from predominantly heterolytic for X-PhCH2CCl with electron-donating X (with developing positive charge on the benzylic carbon in the transition state) to predominantly homolytic for carbenes with electron-withdrawing X. This idea was supported by computational studies.

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“…All of the unsymmetrical hydrazides (R 1 OCONHNHCO 2 R 2 ) were synthesized by condensing a carbazate (R 1 OCONHNH 2 ) with a suitable acylating agent (R 2 OCOX) derived from the alcohol (R 2 OH). The key fluorous carbazate 13 was synthesized by condensing the chloroformate derived from perfluorooctyl propanol 12 and excess hydrazine (eq 4) . Under optimized conditions, this reaction gave the carbazate 13 in 85−91% yields on a 3 g scale.…”

Section: Resultsmentioning

confidence: 99%

Second Generation Fluorous DEAD Reagents Have Expanded Scope in the Mitsunobu Reaction and Retain Convenient Separation Features

Dandapani

Curran

2004

J. Org. Chem.

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First generation fluorous DEAD reagent bis(perfluorohexylethyl)azo dicarboxylate (C(6)F(13)(CH(2))(2)O(2)CN=NCO(2)(CH(2))(2)C(6)F(13), F-DEAD-1) has been shown to underperform relative to diisopropylazodicarboxylate in difficult Mitsunobu reactions involving hindered alcohols or less acidic pronucleophiles (phenols). Two new second generation fluorous reagents bearing propylene spacers instead of the ethylene spacers show expanded reaction scope while retaining the easy fluorous separation features. Byproducts from "half fluorous" reagent perfluorooctylpropyl tert-butyl azo dicarboxylate (C(8)F(17)(CH(2))(3)O(2)CN=NCO2(t)Bu, F-DEAD-2) can be removed by fluorous flash chromatography, and byproducts from bis(perfluorohexylpropyl)azo dicarboxylate (C(6)F(13)(CH(2))(3)O(2)CN=NCO(2)(CH(2))(3)C(6)F(13), F-DEAD-3) can be removed by fluorous solid-phase extraction. The new reagents promise to provide general and complementary solutions for separation problems in Mitsunobu reactions without restricting reaction scope.

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Benzylo×y(4-substituted benzylo×y)carbenes. Generation from o×adiazolines and fragmentation to radical pairs in solution

Cited by 8 publications

References 0 publications

Synthesis, Characterization, and Reactivity of Group 4 Metalloporphyrin Diolate Complexes

Synthesis, Characterization, and Reactivity of Group 4 Metalloporphyrin Diolate Complexes

A Duality of Mechanisms for the Fragmentation of Substituted Benzyloxychlorocarbenes

Second Generation Fluorous DEAD Reagents Have Expanded Scope in the Mitsunobu Reaction and Retain Convenient Separation Features

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