Bicyclo heptane derivs

Scheme 1.24. Lewis acid-catalyzed cationic domino cyclization to give bicyclo[2.2.1]heptane derivatives.

Quin, L.D. and Littlefield, L.B., Importance of the structure of the phosphorus functionality in allowing dihedral angle control of vicinal 13C-31P coupling. Carbon-13 NMR spectra of 7-substituted bicyclo[2,2,l]heptane derivatives,. Org. Chem., 43, 3508, 1978. 

From a mechanistic point of view, the titanocene(II)-promoted intramolecular cyclopro-panation of gem-dihalides possessing a terminal double bond is interesting. Although the products of ring-closing metathesis, i. e. cycloalkenes, are produced in certain cases, the treatment of 6,6- and 7,7-dihalo-l-alkenes (e. g. 39 and 40) with titanocene(II) species affords bicyclo[3.1. OJhexane and bicyclo[4.1.0]heptane derivatives 41 and 42, respectively (Scheme 14.19) [34],... 

Aqueous NaOH (4%, 4 ml) is added to the 3-acylcoumarin (l mmol), phenacyl bromide (0.2 g, 1 mmol) and Aliquat (10 mg, 0.02 mmol) in PhH (4 ml) at 25 °C and the mixture is stirred for 30 min and then poured into ice/H20 (50 ml). The aqueous mixture is neutralized with cone. HC1 and extracted with CHC1, (3 x 20 ml). The extracts are washed with H20, aqueous Na2C03 (sat. soln.), and H20, dried (Na2S04), and evaporated to yield the bicyclo[4.10]heptane derivative. 

In the NMR spectra of 7-azabicyclo[2.2.1]heptane derivatives, the apparent absence of spin-spin coupling between the bridgehead protons and endo protons at C-2 and C-3 (J < IHz) is a consequence of the dihedral angle between the respective C-H bonds being 80°. exo-Protons at C-2 and C-3, however, couple observably with those at the adjacent bridgehead positions, and this difference has proved very useful for assignment of exo or endo stereochemistry to substituents. The same situation applies to bicyclo[2.2.1]heptane and 7-thiabicyclo-[2.2.1]heptane derivatives, which clearly have very similar geometry. 

On the other hand, acyclic diastereomers are not necessarily compounds without any cyclic structural element, but the fragment connecting the stereogenic centers is acyclic. For example, a bicyclo[2.2.1]heptane derivative with a chiral side-chain attached to a nonbridgehead carbon belongs to this second category of acyclic diastereomers. 

As discussed, electron-donating groups at Cl in bicyclo[2.2.1]heptane systems promote the rearrangement to bicyclo[3.1.1]heptane derivatives. Photolysis of 1-methyl bicyclo[2.2.1]heptan-2-one tosylhydrazone in 1,2-dimethoxyethane in the presence of sodium hydroxide gave 2-methyl-bicyclo[3.1. l]heptan-2-ol (26a) in 7.5% yield in addition to bicyclo[2.2.1]heptane derivatives, while the 1-phenyl derivative gave the ring-contracted product 26b in only 2% yield.91... 

Several bicyclo[2.2.1]heptane derivatives with a 1,4-dicarbonyl moiety undergo C—C bond cleavage via intramolecular pinacol coupling, promoted by samar-ium(II) iodide.190... 

The double sequence of dehydrohalogenation of a 7,7-dihalobicyclo[4.1.0]heptane derivative to give a bicyclo[4.1.0]hept-l(7)-ene, followed by base-induced prototropic shifts to move the double bond into the six-membered ring132-141, finds continuing applications in routes to cycloproparenes100,142 ... 

An alternative synthesis of ( )-sesquifenchene (53) has been described27 in which stereoselective methylation of an appropriate bicyclo[2,2,l]heptane derivative (52) is the key step (Scheme 11). Isoepicampherenol (54), a sesquiterpenoid whose... 

The solvolytic behaviour of C(3)-substituted 2a,5-epoxy- and 2a,5-epithio-5a-cholestanes has been compared with that of the simple bicyclo[2,2,0]heptane derivatives, and their 7-oxa- and 7-thia-analogues. The 3a-(cxo)mesylates solvolysed at unexceptional rates, with migration of the anti-periplanar C(l)-C(2) bond resulting in ring contraction to give A-nor products (see p. 298). The... 

Oxidation of bicyclo[3.1.1]heptane derivatives containing an endocyclic double bond results selectively in the frans-oxirane 50 with respect to the geminal dimethyl bridge. The two diastereomers 51 and 52 are obtained from an exocyclic double bond. Menthenone yields exclusively C S-(+)-menthenone oxide 53, with known absolute configuration. ... 

The low-temperature stability of bicyclo[2.2.1]heptane derivatives is well documented by the huge literature on liquid-phase norbornyl carbonium chemistry under such conditions, no ring expansion is observed, but instead, multiple Wagner-Meerwein rearrangements take place, preserving the bicyclo[2.2.1]heptane structure in the course of nucleophilic substitution or elimination reactions. This remarkable behavior is at the origin of the nonclassic carbonium ion concept (28). 

For this transformation, the presence of the oxygen atom in the chain is essential, since oxidative cyclization of methyl 3-oxohept-6-enoate under similar experimental conditions gave a six-membered ring product rather than a bicyclo[4.1.0]heptane derivative. The presence of a heteroatom in the chain is known to facilitate the exo cyelization mode. ... 

The thermal allylidenecyclopropane rearrangement, applied to bicyclo[4.1.0]heptane derivatives leads via a remarkable double ring expansion, to bicyclo[5.3.0]decane derivatives, particularly hydrazulenes. The rearrangement took place with significant stereocontrol making many synthetically useful transformations accessible (Table 8). 

Similarly, cyclopropanation of cycloalkenes and regioselective opening of the three-membered ring can be used in ring-expansion procedures. In the presence of a catalytic amount of bis(acrylonitrile)nickel(0), bicyclo[2.1.0]pentane reacts under mild conditions (40-60 C) with various electron-deficient alkenes, such as methyl acrylate, acrylonitrile, dimethyl maleate and fumarate to give bicyclo[2.2.1]heptane derivatives. An analogous thermal reaction of bicyclo[2.1.0]pentane with, e.g. fumaronitrile, requires much higher temperatures (160°C). ... 

Brinker et al. have studied the insertion of dihalocarbenes into the C-H bonds of bicyclo[3.1.0]hexane and bicyclo[4.1.0]heptane derivatives, both experimentally and theoretically. The reactivity of a specific C-H bond was shown to depend on the ability of the effective delocalization by the alkyl moiety of the partial positive charge that builds up during the insertion step (141 and 142). As a consequence, all factors stabilizing the corresponding carbocation would stabilize the transition state. For example, the insertion of dichlorocarbene into cyclopropane derivatives occurs regio- and stereospecifi-cally [Eqs. (6.129) and (6.130)]. The predominant formation of products 145 and 146, that is, the insertion of CbC into the exo and endo a-C-H bonds, respectively, results from the maximum orbital overlap of the Walsh orbital of the cyclopropane ring and the cx-C-H bond of suitable steric arrangement. 

Reactions of Phosphoranes.—Dimethyl(trichloro)phosphorane (94) reacts with 1-acetylsemicarbazides to form the bicyclic phosphoranes (95). . Y-Ray analysis of the bicyclo[3,2,0]heptane derivative reveals a distorted tbp structure for (95). 

The potential of intramolecular cyclopropanation for the construction of fused-ring carbocycles was first reported in 1961 by Stork and Ficini [38] who showed that copper-catalyzed cychzation of a simple diazoketone derived from 5-hexe-noic acid produced a bicyclo[4.1.0]heptane derivative, Eq. (16). 

Dienophile. The reagent (3) reacts with cyclopentadiene (4) in boiling dioxane to give the endo-bicyclo[2.2. l]heptane derivative (5), which on treatment with either acid or alkali gives the a-dione (6) ... 

Figure 5.50 shows the LUMOs of three bicyclo[2.2.1]heptane derivatives (camphor and norcamphor, above, also have this carbon skeleton). The LUMOs are shown here as 3D regions of space, rather than mapping them onto a surface as was done in Fig. 5.49. Comparing the composite molecule (Fig. 5.50(c)) with the cation and the alkene clearly shows electronic intmction between the p orbital of the cationic carbon and the antibonding MO of the double bond.

Berberine alkaloids synthesis steps, 295-297 Betaines in Wittig olefinations, 29-30 Bicyclic compounds. See Oligocyclic compounds Bicyclic hydrocarbon derivs. pr., 192 Bicyclo[4.1.0]hepta-2,4-dienes rearr., 334 Bicyclo[2.2.1]heptane derivs. pr., 192... 

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