Polyfluorobicyclo[2,2,2]octanes. Part III. Syntheses and reactions of new mono- di- and trihydrides and derived compounds

Fluorobicyclo[2,2,2]octanes as follows were made by fluorination with cobaltic fluoride :- 1H- and 2H- tridecafluoro- ; 1H,2H-, 1H,3H-, 2H,2H-, 2H,3H-, and 1H,4H- dodecafluoro-; 1H,2H,3H-, 1H,2H,4H-, and 1H,3H,3H- undecafluoro-; 2H,2H,3H,3H- decafluoro-. These afforded, by the appropriate dehydrofluorinations, dodecafluoro-; 1H- and 2H- undecafluoro-; 1H,2H-, 1H,3H-, and 1H,4H- decafluoro- bicyclo[2,2,2]oct-2-ene. Self-consistent nmr data confirmed all structures. 1H-Trideca- and 1H,4H-dodeca- fluorobicyclo[2,2,2]octanes possess acidic bridgehead hydrogens, which are reactive under basic conditions, and may be replaced by various functional groups. 1-Lithiotridecafluorobicyclo[2,2,2]octane, a remarkably stable perfluoroalkyl lithium derivative, survived many hours in refluxing ether, but slowly decomposed to 1- substituted undecafluorobicyclo[2,2,2]oct- 2-enes, via a transient intermediate, a bridgehead ‘olefin’ ‘violating’ Bredt's rule.     

8-phosphabicyclo[3.2.1]octanes—II: The synthesis and stereochemistry of 8-phosphabicyclo[3.2.1]oct-6-enes

Several new 8-phosphabicyclo[3.2.1]oct-6-enes and -6-en-3-yl acetates were prepared by the alkyl (or aryl)dihalophosphane addition to cyclohepta -1,3-diene and 1-acetoxy cyclohepta-3,5-diene. The P-configuration in two P-epimer pairs (3, 4 and 5, 6) and three other compounds which were each obtained as a single isomer (1, 2 and 7) was determined by investigation of the NMR spectra, i.e. by complexation of the compounds with Eu(dpm)₃ as well as from the various phosphorus-hydrogen coupling constants. Compounds possessing the same P-substituent were correlated among themselves and in the case of the PPh bearing compounds (1 and 7) further correlation to a known compound (8a) was established. The chemical behaviour of the C₆C₇ double bond is discussed and compared with the corresponding behaviour in trop-6-enes. Great steric hindrance was found for this bond, for which the following sequence is suggested:

The synthesis of a phosphaatropine analog is described.     

Thermal chemistry of bicyclo[4.2.0]oct-2-enes

At 300 degrees C, bicyclo[4.2.0]oct-2-ene (1) isomerizes to bicyclo[2.2.2]oct-2-ene (2) via a formal [1,3] sigmatropic carbon migration. Deuterium labels at C7 and C8 were employed to probe for two-centered stereomutation resulting from C1-C6 cleavage and for one-centered stereomutation resulting from C1-C8 cleavage, respectively. In addition, deuterium labeling allowed for the elucidation of the stereochemical preference of the [1,3] migration of 1 to 2. The two possible [1,3] carbon shift outcomes reflect a slight preference for migration with inversion rather than retention of stereochemistry; the si/sr product ratio is approximately 1.4. One-centered stereomutation is the dominant process in the thermal manifold of 1, with lesser amounts of fragmentation and [1,3] carbon migration processes being observed. All of these observations are consistent with a long-lived, conformationally promiscuous diradical intermediate.     

Thermal reactions of 8-methylbicyclo[4.2.0]oct-2-enes: competitive diradical-mediated [1,3] sigmatropic, stereomutation, and fragmentation processes

[reaction: see text] At 275 degrees C, 8-exo-methylbicyclo[4.2.0]oct-2-ene (1a) undergoes a [1,3] sigmatropic rearrangement to 5-methylbicyclo[2.2.2]oct-2-enes, of which the orbital symmetry-allowed si product is only marginally favored over the forbidden sr product; that is, si/sr is 2.4. Accompanying the [1,3] shift are significant amounts of epimerization and fragmentation. The 8-endo epimer 1b, which yields no [1,3] product, experiences primarily direct fragmentation and secondarily epimerization. A diradical intermediate can account for all such observations.     

A Stereoselective Preparation of 1,2,7-Triazabicyclo[3.3.0]oct-2-enes

5-(Alkylamino)methyl-2-pyrazolines react with ketones or aldehydes to give 1,2,7-triazabicyclo-[3.3.0]oct-2-enes in high yields. The reaction gives only one diastereomer with various aldehydes, except for CH₃CHO.     

Gold-catalyzed tandem 1,3-migration/[2 + 2] cycloaddition of 1,7-enyne benzoates to azabicyclo[4.2.0]oct-5-enes

A synthetic method that relies on gold(I)-catalyzed tandem 1,3-migration/[2 + 2] cycloaddition of 1,7-enyne benzoates to prepare azabicyclo[4.2.0]oct-5-enes is described.     

Reactions of Substituted 2,3,7-Triazabicyclo[3.3.0]oct-2-enes and 1,2,7-Triazaspiro[4.4]non-1-enes with Halogens

Halogenation of 1-substituted 7-aryl-2,3,7-triazabicyclo[3.3.0]oct-2-ene-6,8-diones gives different products, depending on the substituent in position 1 (R¹): when R¹ = Ar, 6-chloro-3-azabicyclo[3.1.0]hexanes are formed, while compounds with R¹ = H or Me give rise to 2- or 4-chloro-2,3,7-triazabicyclo[3.3.0]oct-2-ene-6,8-diones whose thermolysis leads to formation of the corresponding 6-chloro-3-azabicyclo[3.1.0]hexanes. Chlorination of 7-aryl-1,2,7-triazaspiro[4.4]non-1-ene-6,8-diones yields 3-chloro-1,2,7-triazaspiro[4.4]non-1-ene-6,8-diones, and thermolysis of the latter affords 1-chloro-5-azaspiro[2.4]heptanes.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 1, 2005, pp. 78–88.Original Russian Text Copyright © 2005 by Molchanov, Stepakov, Kostikov.     

Thermal reactions of 7-d- and 8-d-bicyclo[4.2.0]oct-2-enes

The gas phase thermal reactions exhibited by bicyclo[4.2.0]oct-2-ene and 7-d and 8-d analogues at 300 degrees C have been followed kinetically through GC and 2H NMR spectroscopic analyses. In contrast to the pattern of transformations exhibited by bicyclo[3.2.0]hept-2-ene and deuterium-labeled analogues, no reactions initiated by C1-C6 bond cleavage are seen, epimerization at C8 is much faster than [1,3] shifts leading to bicyclo[2.2.2]oct-2-ene, and the ratio of rate constants for [1,3] carbon migration with inversion versus migration with retention is approximately 1.4. Homolysis of C1-C8 to give a conformationally flexible diradical intermediate having a relatively long lifetime and multiple options for further reaction (re-formation of C1-C8 with or without net epimerization, fragmentation to 1,3-cyclohexadiene and ethylene, migration to the original C3 with inversion or retention) accords well with the observations. Clearly, orbital symmetry control does not govern stereochemistry for the [1,3] sigmatropic carbon shifts.     

Bicyclo[3.2.1]oct-6-enes via (3+2)cycloaddition

(3+2)Cycloaddition of alkynes to allyl cations, generated from 3-chlorocyclohexenes and zinc chloride, provides a simple and direct route to bicyclo[3.2.1]oct-6-enes.     

Alkoxide-Accelerated [1,3] Sigmatropic Shift of Bicyclo[3.2.1]oct-6-en-2-ols to 8-endo-Hydroxybicyclo[3.3.0]oct-2-en-4-ones

Bicyclo[3.2.1]oct-6-en-2-ols 6 are shown to undergo [1,3] sigmatropic shift to afford 8-endo-hydroxy-bicyclo[3.3.0]oct-2-en-4-ones 8 under the influence of potassium hydride.     

Nuclear magnetic resonance spectra of polyfluorobuta-1,3-dienes. Part II [1]. Variable temperature study of two 2-azabutadienes

The two perfluoro-azadienes CF₂N.CRCF₂ (R = CF₃ or CF₂Cl) show temperature dependent ¹⁹F n.m.r. spectra, with non-equivalent fluorine nuclei of the CF₂N portion at low temperatures, which coalesce due to inversion at the nitrogen at higher temperatures (ΔG3 = 60 kJ mol^?1). N.m.r. parameters have been obtained. One of the five-bond FF coupling constants is much larger ($\text{ca}$. 24 Hz) than the remainder (0·5–5·5 Hz), possibly due to ‘through-space’ coupling of fluorines in the $\text{cis}$-skew conformation.     

Nickel-catalyzed dehydrogenative [4 + 2] cycloaddition of 1,3-dienes with nitriles

Pyridines, which comprise one of the most important classes of the six-membered heterocyclic compounds, are widely distributed in nature, and the transition-metal-catalyzed [2 + 2 + 2] cycloaddition reaction of two alkynes and a nitrile is one of the most powerful methods for preparing versatile, highly substituted pyridine derivatives. However, the lack of chemo- and regioselectivity is still a crucial issue associated with fully intermolecular [2 + 2 + 2] cycloaddition. The present study developed the Ni(0)-catalyzed intermolecular dehydrogenative [4 + 2] cycloaddition reaction of 1,3-butadienes with nitriles to give a variety of pyridines regioselectively.     

Polyfluorobicyclo[4,4,0]decanes. Part I. The fluorination of tetralin over cobalt trifluoride

Fluorination of tetralin over cobalt trifluoride at 250° in a stirred reactor gave the known cis- and trans- perfluorodecalins and two known fluorobicyclo[4,4,0]dec-1(6)-enes. Also obtained were five new heptadecafluorobicyclo[4,4,0]decanes. Dehydrofluorinations of these gave five new hexadecafluorobicyclo[4,4,0]decenes of which one, the 1(2)- isomer, rearranged readily to the 1(6)- isomer.     

One-bond, two-bond, and three-bond mechanisms in thermal deazetizations of 2,3-diazabicyclo[2.2.2]oct-2-enes, trans-azomethane, and 2,3-diazabicyclo[2.2.1]hept-2-ene

The thermal deazetizations of a series of substituted 2,3-diazabicyclo[2.2.2]oct-2-enes and some simpler model systems have been studied using the UB3LYP/6-31G(d) and CASPT2 methods, with a variety of active spaces. A fused cyclopropane exerts unique control on the mechanism and rate of deazetization. When the Walsh sigma-orbitals are appropriately aligned in an exo orientation, a pericyclic three-bond cleavage occurs. For an endo-fused cyclopropane, sequential one-bond cleavages occur to take advantage of orbital overlap with the Walsh orbitals. In systems lacking strongly directing substituents, concerted two-bond cleavage pathways to form diradical intermediates have a small enthalpic advantage (DeltaH(0K)++) over sequential one-bond cleavage pathways. However, the one-bond mechanism has an entropic advantage over the two-bond; consequently, at 400-500 K where decomposition occurs, one-bond and two-bond diradical cleavages both occur simultaneously. The thermal decompositions of trans-azomethane and 2,3-diazabicyclo[2.2.1]hept-2-ene are also studied, and the results are compared to extensive computational studies in the literature. Comparisons of UB3LYP, CASSCF, and CASPT2 surfaces for these reactions are made.