Fragmentation of cyclopropylmethoxychlorocarbene: Formation of cyclopropylcarbinyl/chloride ion pairs

Moss, Robert A.; Ho, Guo Jie; Wilk, Bogdan K.

doi:10.1016/s0040-4039(01)80428-7

Cited by 22 publications

(23 citation statements)

References 16 publications

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“…The extreme value of the chemical shift suggests that it is due to a NH located on the same side (as defined by a plane through C(l) and the two N) as BnO-C (2), and the shielding suggests that it is not in the vicinity of the 0-C(2), hence located below the plane of the pyranose ring (pseudoaxial). The relative chemical shift of H-C(3) and H-C(5) is in agreement with this assignment, in that H-C(3) and H-C (5) of the major isomer 38a resonate at 3.56 and 3.81 ppm, respectively, while the corresponding signals for38b are found at 3.91 and 3.25 ppm, in keeping with the deshielding effect of the nearby N-atom lone pair [62]. The significant low-field shift of AcNH (AS = 0.88 ppm) in the minor isomer 47b may result from an interaction with the lone-pair of a N-atom of the diaziridine ring 1621.…”

supporting

confidence: 85%

“…The activation enthalpies for the thermolysis of 1 and 8 differ by only 0.4 kcal/mol, and the activation entropy by 4.8 e.u. The 1,3-dioxane ring in 9 is expected to lower E,, as the conformational change from a 4C, in the direction of a B2, 5 implies that the axial BnO-C(3) group moves towards a pseudoequatorial position. Also, one expects A S # to be negative.…”

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confidence: 99%

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Glycosylidene Carbenes. Part 13. Synthesis and thermolysis of representative 1‐azi‐glycoses

Vasella

Witzig

Waldraff

et al. 1993

Helvetica Chimica Acta

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Dedicated to Duilio Arigoni on the occasion of his 65th birthday (1.X.93)In the context of the hypothesis postulating a heterolytic cleavage of a C-N bond during thermolysis of alkoxydiazirines (Scheme I ) , we report the preparation of the diazirines4,5,7, and 8, the kinetic parameters for the thermolysis in MeOH of the diazirines 1 and 4-9, and the products of their thermolysis in an aprotic environment. The diazirines 4,5,7, and 8 (Schemes 2-5) were prepared from the known hemiacetals 10,19,34 (prepared from 31 in an improved way), and 42 according to an established method. The oximes 11,20,35, and 43 were obtained from the corresponding hemiacetals as (E/Z)-mixtures; 43 was formed together wlth the cyclic hydroxylamine 44. Oxidation of 11,35, and 43 (N-chlorosuccinimide/l,8-diazabicyclo[5.4.0]undec-7-ene (NCS/DBU) or NaIO,) gave good yields of the (Z)-hydroximolactones 12, 36, and 45, while the oxime 20 led to a mixture of the (E)-and (2)-hydroximolactones 21 and 22, which adopt different conformations. Their configuration was assigned, inter alia, by a comparison with the enol ethers 28 and 29, which were obtained, together with 30, from the reaction of the diazirine 5 with benzaldehyde and PBu,. Treatment of the hydroximolactone 0-sulfonates 13,23,37, and 46 with NH,/MeOH afforded the diaziridines 15,25,38, and 47 in good yields, while the (E)-sulfonate 24 decomposed readily. Oxidation of the diaziridines gave 4, 5, 7, and 8, respectively. Thermolysis of the diazirines 1 and 4-9 in MeOH yielded the anomeric methyl glycosides 50/51,16/17,26/27,52/53,39/40,48/49, and 54/55, respectively. A comparison of the kinetic data of the thermolysis at four different temperatures shows the importance of conformational and electronic factors and is compatible with the hypothesis of a heterolytic cleavage of a C-N bond. An early transition state is evidenced by the absence of torsional strain by an annulated 1,3-dioxane ring. Thermolysis of 1 in MeCN at 23" led mostly to the diastereoisoineric (Z,Z)-, (E,E)-, and (E,Z)-lactone azines 56, 57, and 58 (Scheme 6), which convert to 56 under mild conditions, and to 59 (3%). The benzyloxyglucal59 was obtained in higher yields (IS%), together with 44% of 5658, by thermolysis of solid 1. Similarly, thermolysis at higher temperatures of4 in toluene, THF, or dioxane and of 9 in CH2C12 or THF yielded the (Z,Z)-lactone azines 60 and 61, respectively, the latter being accompanied by the dihydro-oxazole 62.Introduction. -Diazirines [I] are important precursors of carbenes, and the mechanism of their thermolysis attracted considerable attention, which focused on the concertedness of the cleavage of the two C-N bonds and the homo-or heterolytic nature of the bond breaking [2-71. The mechanism and the kinetics of the thermolysis of (a1koxy)alkyldiazirines (see [8] and earlier papers of the series [9-131) have not been studied, but we hypothesized that thermolysis of 1-azisugars, such as 1, i.e. cyclic (alkoxy)alkyldiazirines, is initiated by heterolysis of one of the C( 1)-N bonds, accord-

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supporting

confidence: 85%

mentioning

confidence: 99%

Glycosylidene Carbenes. Part 13. Synthesis and thermolysis of representative 1‐azi‐glycoses

Vasella

Witzig

Waldraff

et al. 1993

Helvetica Chimica Acta

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“…14,16 However, the cyclopropylmethyl cation generated as part of the tight ion pair in eq 6 affords only limited CH 2 scrambling. 15 The case for ion pair intervention in eq 6 is strengthened if we recall Skell's analogy to the chemistry of alkyldiazonium ions. 2 Thus, the reactions (in ether) of cyclopropyldiazomethane with benzoic acid, or of cyclopropylmethyl diazotate with benzoyl chloride, afford cyclopropylmethyl benzoate ion pairs 13, which yield the benzoate analogues of 10-12 in distributions very similar (79:14:7 or 78:13:9) to those of the cyclopropylmethyl cation-carbon monoxide-chloride ion pair of eq 6.…”

Section: Cyclopropylmethoxychlorocarbenementioning

confidence: 99%

“…Although ROCCl (and ROCBr) readily fragment, there are closely related species that do not. Examples include phenoxychlorocarbene (14) and benzyloxyfluorocarbene (15) Phenoxychlorocarbene resists fragmentation because scission to an ion pair (Ph + OC Cl -) would produce the high-energy phenyl cation. Carbene 14, therefore, behaves as a typical ambiphile, offering a variety of intermolecular reactions.…”

Section: Alkoxyfluorocarbenesmentioning

confidence: 99%

“…Carbene 14, therefore, behaves as a typical ambiphile, offering a variety of intermolecular reactions. 19 Benzyloxyfluorocarbene (15), generated by thermolysis of the appropriate diazirine at 80 °C in MeCN, gave less than 10% of fragmentation to PhCH 2 F; the major products corresponded to HF or H 2 O trapping of the carbene. 20 Under comparable conditions, PhCH 2 OCBr completely fragmented to PhCH 2 Br.…”

Section: Alkoxyfluorocarbenesmentioning

confidence: 99%

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The Fragmentation of Alkoxyhalocarbenes

Moss

1999

Acc. Chem. Res.

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Alkoxyhalocarbenes stand at an intersection of carbene, carbocation, elimination, and substitution chemistry. Their fates are decided by several fundamental mechanisms, and we can anticipate significant contributions to mechanistic organic chemistry from an understanding of their behavior. In the 1950s, Hine 1 and Skell 2 reported that dihalocarbenes reacted with alkoxides to form alkoxyhalocarbenes, 1, and Skell suggested that, when sec-or tert-alcohols were used, the derived carbenes fragmented to alkyl cations with the loss of CO and X -(eq 1, X ) Cl or Br). Noting the close resemblance between CO and N 2 , Skell offered an analogy between reaction 1 and the decomposition of alkyldiazonium ions (RN 2 + f R + + N 2 ).

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ChemInform Abstract: Fragmentation of Cyclopropylmethoxychlorocarbene: Formation of Cyclopropylcarbinyl/Chloride Ion Pairs.

Moss

Wilk

1989

ChemInform

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Fragmentation of cyclopropylmethoxychlorocarbene: Formation of cyclopropylcarbinyl/chloride ion pairs

Cited by 22 publications

References 16 publications

Glycosylidene Carbenes. Part 13. Synthesis and thermolysis of representative 1‐azi‐glycoses

Glycosylidene Carbenes. Part 13. Synthesis and thermolysis of representative 1‐azi‐glycoses

The Fragmentation of Alkoxyhalocarbenes

ChemInform Abstract: Fragmentation of Cyclopropylmethoxychlorocarbene: Formation of Cyclopropylcarbinyl/Chloride Ion Pairs.

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