The thermal isomerization of cyclopropylcarbinyl thiocyanate

Spurlock, Langley A.; Newallis, Peter E.

doi:10.1016/s0040-4039(01)99651-0

Cited by 5 publications

(3 citation statements)

References 6 publications

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“…9 Alkyl thiocyanates that do not form carbenium ions readily tend not to isomerize. 8,10 Methyl thiocyanate rearranges to the isothiocyanate in a sealed tube at 180−185 °C, 11 and it has also been reported to rearrange slowly at its boiling point, 131 °C. 8 Allylic thiocyanates are extremely unstable, because they undergo facile [3,3]-sigmatropic rearrangements, which have been investigated by several authors.…”

Section: ■ Introductionmentioning

confidence: 99%

“…An ion pair mechanism has also been advanced for the isomerization of alkyl cyanates ROCN to isocyanates RNCO . Alkyl thiocyanates that do not form carbenium ions readily tend not to isomerize. , Methyl thiocyanate rearranges to the isothiocyanate in a sealed tube at 180–185 °C, and it has also been reported to rearrange slowly at its boiling point, 131 °C …”

Section: Introductionmentioning

confidence: 99%

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Rearrangements of Acyl, Thioacyl, and Imidoyl (Thio)cyanates to Iso(thio)cyanates, Acyl Iso(thio)cyanates to (Thio)acyl Isocyanates, and Imidoyl Iso(thio)cyanates to (Thio)acyl Carbodiimides, RCX-YCN ⇌ RCX-NCY ⇌ RCY-NCX ⇌ RCY-XCN (X and Y = O, S, NR′)

Koch

Wentrup

2012

J. Org. Chem.

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Two types of rearrangements have been investigated computationally at the B3LYP/6-311+G(d,p) level. The activation barriers for rearrangement of acyl thiocyanates RCO-SCN to the corresponding isothiocyanates RCO-NCS are 30-31 kcal/mol in agreement with the observation that the thiocyanates are in some cases isolable albeit very sensitive compounds. Alkoxycarbonyl-, (alkylthio)carbonyl- and carbamoyl thiocyanates are isolable and have higher calculated barriers (ca. 40 kcal/mol) toward rearrangement to isothiocyanates, whereas all thioacyl thiocyanate derivatives are rather unstable compounds with barriers in the range 20-30 kcal/mol for rearrangement to the isothiocyanates. Acyl-, alkoxycarbonyl-, and carbamoyl cyanates R-CO-OCN are predicted to be in some cases isolable compounds with barriers up to ca. 40 kcal/mol for rearrangement to the isocyanates RCO-NCO. All of the rearrangements of this type involve the HOMO of a nearly linear (thio)cyanate anion and the LUMO of the acyl cation, in particular the acyl C═X π* orbital. The second type of rearrangement involves 1,3-shifts of the groups R attached to the (thio)acyl groups, that is, acyl isothiocyanate-thioacyl isocyanate and imidoyl isothiocyanate-thioacyl carbodiimide rearrangements. These reactions involve four-membered cyclic, zwitterionic transition states facilitated by lone pair-LUMO interactions between the migrating R group and the neighboring iso(thio)cyanate function. Combination of the two rearrangements leads to the general reaction scheme RCX-YCN ⇌ RCX-NCY ⇌ RCY-NCX ⇌ RCY-XCN (X and Y = O, S, NR').

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Section: ■ Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Rearrangements of Acyl, Thioacyl, and Imidoyl (Thio)cyanates to Iso(thio)cyanates, Acyl Iso(thio)cyanates to (Thio)acyl Isocyanates, and Imidoyl Iso(thio)cyanates to (Thio)acyl Carbodiimides, RCX-YCN ⇌ RCX-NCY ⇌ RCY-NCX ⇌ RCY-XCN (X and Y = O, S, NR′)

Koch

Wentrup

2012

J. Org. Chem.

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“…Caled for CgHnNS: C, 62.70; H, 7.24; N, 9.14; S, 20.93. Found: C, 62.51; H, 7.29; N, 9.18; S, 20.82. exo-2-Norbornyl Isothiocyanate (6). A 5.00-g (0.045 mole) portion of exo-2-norbomylamine20 was subjected to the previously described procedure affording 5.01 g (72%) of product: bp 81-83°( 2 mm); infrared spectrum (film), 2920, 2080, 1340, 945, and 760 cm"1; nmr (CC14), 6.46 (tr), 7.57 (br s), 7.83-9.42 (mult).…”

Section: Experimental Section18mentioning

confidence: 99%

Nature of the carbonium ion. I. The .pi.-route to a norbornyl cation from a thiocyanate-isothiocyanate isomerization

Spurlock¹,

Cox²

1969

J. Am. Chem. Soc.

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Nmr single resonance spectra were obtained on Varían HA 100 ( ) and A56-50 (18F) spectrometers. ( 19), 19F(!H), and i9p(i»F) double-resonance experiments were performed on a Varían HA-60 instrument operating at 56.4 and 60.0 MHz. Octafluorocyclobutane, CCLF, CF2CICF2CI, and C6H5CF3 were used as lock signals for the 18F experiments. The necessary irradiating field for the heteronuclear decoupling experiments was provided by a NMR Specialties Model SD-60B heteronuclear spin decoupler. All of the benzotrifluorides 5 were obtained from Columbia Organic Chemicals., -DifluorotoIuene was prepared from benzaldehyde and SF4.16 , , -DifluorochlorotoIuene. In a three-necked, 250-ml flask equipped with a thermometer, gas inlet tube, and reflux condenser was placed 30 ml of , -difluorotoluene and 50 mg of azobisisobutyronitrile. The flask was then heated to 70°while chlorine gas was bubbled through the reaction mixture. The reaction was followed by 18F nmr and by testing the effluent gas for HC1 and was found to be over in about 90 min. The product was then distilled: bp 140°, 61°(50 mm); nmr (CC13) multiplet 5 7.5, 19F 49.36.2,3,4,5,6-Pentafluorobenzyl Fluoride. The apparatus consisted of a 250-ml, three-necked flask equipped with an addition funnel, a motor-driven stirrer, and an exit tube leading to a Dry Ice trap connected to a vacuum pump. The apparatus was flushed with dry nitrogen and then 48 g (0.2 mol) of finely powdered HgF2 was placed in the flask and 10 g (0.04 mol) pentafiuorobenzyl bromide (Penninsular Chem Research) was placed in the funnel.After evacuation of the flask the bromide was then added dropwise to the rapidly stirred mercuric fluoride over a period of 15 min. The product which collected in the Dry Ice trap was then filtered from a few grams of NaF, yield 1.8 g (45%). The nmr spectrum is given in Table IV.Decafluorobenzhydrol was obtained from Imperial Smelters Ltd. Tris(pentafluorophenyI)carbinol was a gift from Professor R.

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Umlagerungen von Homoallyl-, von Cyclopropylmethyl- und Cyclobutyl-Verbindungen

Hanack

Schneider

Fortschritte Der Chemischen Forschung

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The thermal isomerization of cyclopropylcarbinyl thiocyanate

Cited by 5 publications

References 6 publications

Rearrangements of Acyl, Thioacyl, and Imidoyl (Thio)cyanates to Iso(thio)cyanates, Acyl Iso(thio)cyanates to (Thio)acyl Isocyanates, and Imidoyl Iso(thio)cyanates to (Thio)acyl Carbodiimides, RCX-YCN ⇌ RCX-NCY ⇌ RCY-NCX ⇌ RCY-XCN (X and Y = O, S, NR′)

Rearrangements of Acyl, Thioacyl, and Imidoyl (Thio)cyanates to Iso(thio)cyanates, Acyl Iso(thio)cyanates to (Thio)acyl Isocyanates, and Imidoyl Iso(thio)cyanates to (Thio)acyl Carbodiimides, RCX-YCN ⇌ RCX-NCY ⇌ RCY-NCX ⇌ RCY-XCN (X and Y = O, S, NR′)

Nature of the carbonium ion. I. The .pi.-route to a norbornyl cation from a thiocyanate-isothiocyanate isomerization

Umlagerungen von Homoallyl-, von Cyclopropylmethyl- und Cyclobutyl-Verbindungen

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