Regioselective Formation of Alkylidenecyclopropanes from 2-Substituted Cyclobutylidenes Generated from Geminal Dibromocyclobutanes and Methyllithium

Nordvik, Tore; Mieusset, Jean‐Luc; Brinker, Udo H.

doi:10.1021/ol036348r

Cited by 19 publications

(16 citation statements)

References 29 publications

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“…[32] In contrast to previous studies using diazocyclobutanes as carbene precursors at temperatures above 200 8C via reaction of the corresponding tosylhydrazone sodium salts, the organometallic route in each case produced an alkylidenecyclopropane as the sole product which could be isolated in good yields, as shown in Scheme 15. B3LYP calculations were employed to rationalize the observed regioselective ring contraction of the generated 2-substituted cyclobutylidenes depicted in Scheme 15.…”

Section: Eliminationsmentioning

confidence: 81%

Synthesis of Methylene‐ and Alkylidenecyclopropane Derivatives

Audran

Pellissier

2010

Adv Synth Catal

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Since the methylenecyclopropane moiety is found in many biologically active natural substances, the synthesis of methylene-and alkylidenecyclopropanes remains a considerable challenge. In addition, an attractive feature is their surprising stability, accompanied by a high level of strain, conferring on them an otherwise unattainable chemical reactivity. The growing interest in the chemistry of these compounds has in its turn stimulated the development of alternative approaches to their skeleton, aimed at selectively introducing structural and chemical diversification. The three principal methods to synthesize these important compounds are based on the formation of the cyclopropane ring, the use of preformed cyclopropanes, and the use of preformed methyleneand alkylidenecyclopropanes.

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Section: Eliminationsmentioning

confidence: 81%

Synthesis of Methylene‐ and Alkylidenecyclopropane Derivatives

Audran

Pellissier

2010

Adv Synth Catal

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“…Indeed, the exo methylene group of 19 casts doubt on its direct formation from 1 . Recall that 2-alkyl-substituted cyclobutylidenes 11 often form alkylidenecyclopropanes 12a regiospecifically . The preference for 12a (Scheme a) can be traced back to its internal C–C double bond, which is more highly substituted than the external C–C double bond of 12b (Scheme b).…”

Section: Resultsmentioning

confidence: 99%

“…Alkylcarbenes often undergo rapid 1,2-H shifts to form alkenes. However, this rearrangement is much less pronounced in 2-alkylcyclobutylidenes (e.g., Scheme d, e). − Spiro[3.3]hept-1-ene ( 22c ) would arise from a 1,2-H shift in 1 (Scheme g). Although there is acute bending of the nominally sp 2 -hybridized C1 and C2 atoms in 22c , angle strain within such a C–C double bond is only a minor barrier toward its formation. ,, If 1 yields vibrationally excited 22c *, then chemical activation would facilitate electrocyclic ring-opening to conjugated diene 22d (Scheme h; cf.…”

Section: Resultsmentioning

confidence: 99%

“…2-Alkylcyclobutylidenes 11 yield alkylidenecyclopropanes and alkylcyclobutenes to a lesser extent (Scheme ). ,− The type of carbene precursor used (e.g., gem -dibromo compound or p -tosylhydrazone alkali salt) and the reaction conditions (e.g., T = −78 to 0 °C/RLi/Et 2 O or T = 120 to 310 °C/ p = (0.1–1.0) × 10 –4 Torr) affect the scope of the isomerizations. For example, the debromination of 2-alkyl-1,1-dibromocyclobutanes produces alkylidenecyclopropanes 12a in high yield (Scheme a), whereas alkylcyclobutenes 12c – e are not formed at all (Scheme c–e) .…”

Section: Introductionmentioning

confidence: 99%

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Competitive 1,2-C Atom Shifts in the Strained Carbene Spiro[3.3]hept-1-ylidene Explained by Distinct Ring-Puckered Conformers

Rosenberg

Schrievers²,

Brinker

2016

J. Org. Chem.

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Spiro[3.3]hept-1-ylidene is a markedly strained carbene reaction intermediate that was generated by high-vacuum flash pyrolysis (HVFP) of the corresponding p-tosylhydrazone sodium salt. Five hydrocarbons were produced from the Bamford-Stevens reactant in 82% overall yield. The carbene undergoes two [1,2]-sigmatropic rearrangements via competing 1,2-C atom shifts. Ring-contraction yields cyclopropylidenecyclobutane, while ring-expansion affords bicyclo[3.2.0]hept-1(5)-ene. The ring contraction is regiospecific despite the formation of some 1-methylenespiro[2.3]hexane. It does not originate from the carbene under HVFP conditions. Instead, it comes from a methylenecyclopropane-type rearrangement of chemically activated cyclopropylidenecyclobutane. Similarly, some chemically activated bicyclo[3.2.0]hept-1(5)-ene rearranges to 1,2-dimethylenecyclopentane via electrocyclic ring-opening. Accounting for the conversion of primary products to secondary ones, relative yields indicate that ring-contraction within the carbene prevails over ring-expansion by a factor of 6.7:1. Computational chemistry was used to assess the structures, conformations, energies, strain energies, transition states, and activation energies of these rearrangements with the goal of explaining product selectivities. The dual-ringed carbene is predicted to assume four distinct geometric conformations that have a bearing on transition-state selection. The reactive cyclobutylidene units of two conformers are significantly puckered, like cyclobutylidene itself, while those of the other two are flatter. The selectivity of the title carbene is compared with that of spiro[2.3]hex-4-ylidene.

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“…In another context, Brinker et al. have developed the regioselective formation of alkylidenecyclopropanes 33a–d from 2‐substituted cyclobutylidenes 34a–d generated from geminal dibromocyclobutanes and methyllithium at −78 °C 32. In contrast to previous studies using diazocyclobutanes as carbene precursors at temperatures above 200 °C via reaction of the corresponding tosylhydrazone sodium salts, the organometallic route in each case produced an alkylidenecyclopropane as the sole product which could be isolated in good yields, as shown in Scheme .…”

Section: Formation Of the Cyclopropane Ringmentioning

confidence: 99%

P111: Bilateral vital tubal ectopic pregnancy detected by color Doppler transvaginal ultrasonography

Jurisic¹,

Andjelic²,

Filipović³

2003

Ultrasound Obstet Gynecol

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Poster abstracts c) Suboptimal: Only mentioned an empty uterus, and nothing else. Results: Of the 52 cases of confirmed ectopic pregnancies, 17 (32.7%) had diagnostic scan reports, 23 (43.3%) were adequately detailed, and 12 (23.1%) were considered suboptimal. Conclusions: An unacceptably high proportion of reports (23.1%) were considered suboptimal. We are now working on a standard reporting format for all early pregnancy ultrasound scans performed in this trust. This will improve communication between practitioners involved in the care of these patients, and improve patient care. In clinically suspected EP cases, when hCG > 2000 mIU/mL and TVCD failed to disclose intrauterine gestational sac, the patient had an EP or RSA. When hCG < 2000 mlU/ml, serial hCG test was performed (on 48 h. intervals) and the TVCD was repeated once the discriminatory level was reached. In cases of MP with ''snow storm'' sign, high vascularization and low RI/PI, a hCG was not decreased (uncommonly increased). After the MP extraction the abovementioned findings were correlated with hCG level. In cases of OH, OR, OT the increased level of hCG was not so significant, as clinical manifestation (pelvic pain) and TVCD findings. P110 Conclusion:The TVCD has significant role in management of patients with positive hCG test. P111 Bilateral vital tubal ectopic pregnancy detected by color Doppler transvaginal ultrasonography A. Jurisic, S. Andjelic and D. Filipovic Narodni front OB/GYN University Clinic, Belgrade, SerbiaBilateral tubal ectopic pregnancies are rare conditions and occur at the incidence 1 : 1000-1 : 1500 ectopic pregnancies. A 29 years old patient with amenorrhoea and positive HCG was referred to our clinic for suspected ectopid pregnancy. Patient had stimulated cycle with Clomiphene citrate. Transvaginal color Doppler ultrasonography showed empty uterus with hyperechogenic endometrium 25 mm thick. Transversal wide angle scan showed ectopic gestational sacs in both tubes. Normal embryos were detected in both gestational sacs and color Doppler ultrasonography confirmed normal embrional heart rate in both ectopic pregnancies. Laparotomy was performed and ectopic pregnancy in isthmic part of the right tube was confirmed. In the left tube ectopic pregnancy was localized in ampulary and isthmic region. Right salpingectomy was performed and on the left side, incision of the tube, expression or the trophoblastic tissue and tubal reconstruction was performed. Histopathological examination confirmed ectopic trophoblastic and embrional tissue on both sides. P112Is the use of prophylactic antibiotics required in women being managed expectantly with incomplete miscarriage? G. Condous, E. Okaro, A. Khalid, S. Rao, M. Alkatib and T. Bourne St George's Hospital Medical School, UKBackground: The use of prophylactic antibiotics has been shown to be of no value in women treated with surgical evacuation for incomplete miscarriage. The use of prophylactic antibiotics has not been prospectively validated in women with incomplete miscarriage who choos...

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Regioselective Formation of Alkylidenecyclopropanes from 2-Substituted Cyclobutylidenes Generated from Geminal Dibromocyclobutanes and Methyllithium

Cited by 19 publications

References 29 publications

Synthesis of Methylene‐ and Alkylidenecyclopropane Derivatives

Synthesis of Methylene‐ and Alkylidenecyclopropane Derivatives

Competitive 1,2-C Atom Shifts in the Strained Carbene Spiro[3.3]hept-1-ylidene Explained by Distinct Ring-Puckered Conformers

P111: Bilateral vital tubal ectopic pregnancy detected by color Doppler transvaginal ultrasonography

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