Bridged bicyclic

Bredt s rule A double bond cannot be introduced at the bridgehead carbon of a bridged bicyclic or polocyclic system with small- or medium-sized rings. 

Cyclic dienes yield bridged bicyclic Diels-Alder adducts... 

The relation of rates of reduction with NaBH4 to variations in structure in a wide variety of monocyclic and bridged bicyclic compounds has also been discussed for example, a methyl a to a ketone slows the rate of reduction. Brown ° stated that reactions should not be discussed in terms of axial and equatorial attack, since the rates simply reflect differences in the energies of the possible transition states and not enough is known about the transition state to analyze it. He accepted th concepts of SAC and PDC, but preferred to call them steric strain contrpl and product stability control. ... 

The reactions of enamines with a,/3-unsaturated acid chlorides have provided bridged bicyclic diketones 312,313). 

The exclusion of nitrogen-bridged bicyclic azines is purely arbitrary since the work on such azinoazines with a 10 7r-electron system (and the necessarily accompanying quaternary nitrogen-bridgehead atom) shows the activation expected of other aromatic azinium... 

Yokoyama, Y. and Hall, H. K. Ring-Opening Polymerization of Atom-Bridged and Bond-Bridged Bicyclic Ethers, Acetals and Orthoesters. Vol. 42, pp. 107—138. 

In bridged bicyclic ring systems, two rings share more than two atoms. In these cases, there may be fewer than 2" isomers because of the structure of the system. For example, there are only two isomers of camphor (a pair of enantiomers), although it has two chiral carbons. In both isomers, the methyl and hydrogen are cis. The trans pair of enantiomers is impossible in this case, since the bridge must be cis. The... 

Ozoe Y, Matsumura F. 1986. Structural requirements for bridged bicyclic compounds acting on picrotoxinin receptor. J Agric Food Chem 34 126-134. 

From the reactions presented in this section one can conclude that cyclic acetal formation via addition to a carbene intermediate is a general reaction for type I cleavage of cyclobutanones, tricyclic compounds, and certain bridged bicyclics as minor products. No acetal has been isolated from photolyses of cyclopentanones or cyclohexanones except for the special case of an a-sila ketone previously discussed. 

It has been stated that bridged bicyclic systems fail to yield any cyclic acetal upon photolysis,[Pg.382]

With a synthesis of 58 completed, the key intramolecular diketone aldol cyclization was investigated. Precedent for this type of 1,8-dicarbonyl aldol reaction is rare, although an aldol reaction has been proposed in the biosynthetic pathway to the hypocrellins. The only reported examples of such diketone aldol cyclizations involve multicyclic or bridged bicyclic systems, and of these no examples exist for 1,8-diketones forming 7-membered rings. MM2 calculations indicated that a... 

Scheme 6.97 Copper-catalyzed asymmetric allylic oxidation of bridged bicyclic alkenes.

Bridged bicycles (13), containing different elements, were synthesized using tris(hydroxymethyl)phosphine [Eq. (11)] (65IC1655 70JOC2310 73PS1). 

Photo- and thermal decarbonylation of cyclic unsaturated ketones leads to the formation of cyclic 1,3-dienes. Such decarbonylations are commonly observed in 7-ketonorbomenes and related bridged bicyclic systems to give cyclohexadienes (equation 84)132. 

According to Scheme 2.2Ilf, heating of nitrones (476a,b) in toluene gave bridged bicyclic compounds (477a,b), as the major reaction products (Scheme 2.235) (704). 

The products of these [4 + 2 + 2]-reactions have a high level of molecular complexity, which has been used to advantage in exploring the conversion of the [4 + 2 + 2]-cycloadducts into commonly encountered ring systems. Zeise s dimer, for example, has been employed to carry out a skeletal rearrangement, as illustrated in Scheme 61, producing fused and bridged bicyclic systems found in several natural product families. 

Although cyclizations from the direct anodic oxidation of acyclic 1,3-dicarbonyl compounds have not been reported, the analogous mediated reactions have been studied [24]. Snider and McCarthy compared oxidative cyclization reactions using a stoichiometric amount of Mn(OAc)3 with oxidations using a catalytic amount of Mn(OAc)3 that was recycled at an anode surface (Scheme 11). In the best case, the anodic oxidation procedure led to a 59% yield of the desired bridged bicyclic product with the use of only 0.2 equivalents (10% of the theoretical amount needed) of Mn(OAc)3- Evidence that the reaction was initiated by the presence of the mediator was obtained by examining the electrolysis reaction without the added Mn(OAc)3. In this case, none of the cyclized product was obtained. For comparison, the oxidation using... 

The relative reactivity of a wide series of nucleophiles towards dioxirane, dimethyidioxirane, carbonyl oxide, and dimethylcarbonyl oxide has been examined at various levels of theory. The general trend in reactivity for oxidation by dioxirane was R2S R2SO, R3P > R3N in the gas phase, and R2S R2SO, R3N R3 (R = Me) in solution. A theoretical study of the first oxidation step of [3.2.1]-bridged bicyclic disulfides highlights a highly oriented reaction path was probably responsible for stereoselective attack on the exo face. ... 

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