Bicyclo octene ring

Reactions of Reformatskii products a,/ - thylenecarboxylic acid esters from ketones via / -acetoxycarboxylic acid esters Bicyclo[2.2.2]octene ring fragmentation... 

Bicyclo[4.4.0]octa-l,3,5-trienes s. Benzocyclobutenes Bicyclo[2.2.2]octene ring fragmentation 26,938 Bicyclo[3.2.1]octenes... 

The i yn-preference of 59a is concluded to be attributable to the fused cyclopropyl ring, based on the observation that the bicyclo[2.2.2]octene (59b) fused with a... 

Ring-opening was not restricted just to norbornenes bicyclo[3.3.0]octenes, cyclooctene and a functionalised cyclobutene were all reactive substrates for these reactions. 

Cylindramide (90) is a cytotoxic compound isolated from Halichondria cylindrata (7.10 s % wet wt.), but very likely of bacterial origin [148]. The structure was deduced from spectroscopic analysis, the relative stereochemistry (only) of the bicyclo[3.3.0]octene unit by NOESY techniques, and the absolute stereochemistry of the amino acid of the tetramic acid ring (25,35) from the recovery of erythtro-L-(3-hydroxyomithine from oxidative degradation of 90. It showed cytotoxicity to B16 melanoma cells (IC50 0.8 (ig/ml). 

The most popular Cope substrates of this class, represented by (127), can be considered relatives of 1,2-divinylcycloalkanes in which an additional carbon-Concerted Cope rearrangement of (127) is permitted as long as the vinyl group is endo, and leads to a fused bicyclic diene (128), necessarily cis. The ring systems most frequently employed have been bicyclo[2.2. Ijheptenes ix = y= 1). leading to hydroindenes, and bicyclo[2.2.2]octenes (j = 2, y = 1), which afford cu-decalin skeletons. Examples of the former are shown in equation (88) and the latter is illustrated in Scheme 5 (52 - 53). 

Oxymercaration (2, 265-267 3. 194). Brown and Geoghegan have investigated the relative reactivities of a number of olefins in the oxymercuration reaction in a 20 80 (v/v) mixture of water and THF. The following reactivity is observed terminal disubstituted > terminal monosubstituted > internal disubstituted > internal trisub-stituted > internal leirasubstitu ted. Thus steric factors play a major role in the reactivity of olefins. Increased substitution on the double bond and increased steric hindrance at the site of hydroxyl or mercury substituent attachment decrease the rate of reaction. In the case of olefins of the type RCH CHR, cts-oleiins are more reactive than the corre.sponding rra/i.s-olefins. Inclusion of the double bond in ring systems causes a moderate rate increase which varies somewhat with structure cyclohcxenc > cyclo-pentenc cyclooctene norbornene bicyclo[2.2.2]-octene-2. 

In fact, whenever the primary carbonium ion is formed from the proper substrate, ring expansion is observed this is the case in the acid-catalyzed dehydration of 2-hydroxymethylbicyclo[2.2.1]heptane (23), producing a mixture of 2.5% methylenebicyclo[2.2.1]heptane (7), 87% bicyclo[3.2.1]-2-octene (5), and 10% bicyclo[3.3.0]-2-octene (6) and in the nitrous acid deamination of 2-aminomethylbicyclo[2.2.1]-heptane to bicyclo[3.2.1]- and bicyclo[2.2.2]octanols 30). 

Building the C-2 oxygen atom into the bicyclo-[2.2.1] ring system seriously distorts x, the O-C-C-N dihedral angle. As shown in Figure 10, rhe benzobicyclo [2. 2. 2 ] octenes provide excellent values for (endo, 59° exo, 56°), but VII forms an 83° angle. 

Molecules containing a bicyclo[2.2.2]octen-2-one subunit fused or bridged to an additional ring have been investigated in detail, as their oxa-7c-methane rearrangements afford tetracyclic ketones, usually in very good yields. The commonest examples are 7,8-fused substrates 33 which afford 6,7-exo-fused tricyclo[3.3.0.0 ]octan-3-ones 34. 

The intra- and intermolecular addition of carbon centered radicals to carbon-carbon double bonds is currently of great synthetic interest and much work has been done for control of regioselectivity (256,257). Comparatively little work has been done to investigate the reactivities of strained olefins. The rates of gas-phase additions of HO" and N03" radicals to the cyclic olefins with ring size 5-7, norbornene (287) and bicyclo[2.2.2]octene (288), showed little variation (krel < 1.8 and krel < 5, respectively) and were insensitive to the ring strain energies (258). 

Grieco and coworkers have utilized intramolecular aldolization of keto aldehydes to form seven-mem-bered rings. In a synthesis of ( )-helenalin, keto aldehyde (54) was cyclized to aldol (55 equation 1In a later modification of the basic approach, keto aldehyde (56) was cyclized to cycloheptenone (57 equation 113).The success of these cyclizations is related to the fact that the normally preferred five-membered ring closure would yield a strained rnzns-fused bicyclo[3.3.0]octene system. 

Hydropentalenes (bicyclo[3.3.0]octanes) are not very common in nature. Therefore, few studies have dealt with the hydrogenation of bicyclo[3.3.0]octenes. However, fused five-membercd rings form the skeleton of the tricyclic triquinanes. Furthermore, in all natural products of the triquinane type, the fusion of the five-membered rings is exclusively cis. 

Almost at the same time, we discovered [6] a very efficient formation of a cyclopropane ring via 3-exo trig radical cyclization reactions of bicyclo[2.2.2]oct-5-en-2-yl and bicyclo[3.2.1]oct-6-en-2-yl bromides 4 and 5. The bromides 4 and 5, obtained from carvone via a common bicyclo[2.2.2]octene precursor, on treatment with... 

This is a bicyclic compound (because the carbon atoms form two rings) consisting of 8 carbon atoms in all, which are numbered as shown. Look at the linkages between Ci and Cs. Four carbon atoms follow Ci(C2 Cs)a while 2 atoms follow Cs (C7 Cs). There are no atoms internal to the Cl - Ce bond itself. Since a chlorine atom is bonded to Ce, we can name this compound as 8-chloro bicyclo[4.2.0]-2-octene. 2-octene signifies the presence of a double bond between C2 and C3 in a 8-carbon compound. 

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