Bicyclo octadiene - from

A number of CSl additions have been shown to produce much less stable j5-lactams. The azetidinone (51) was isolated from the reaction of cyclo-hexadiene with CSI for five minutes at room temperature, while after thirty hours (52) was formed, and the reaction in refluxing chloroform gave (53). Analogous reactions with bicyclo-octadiene did not involve the tautomeric cyclo-octatriene. Initial formation of a 1,4-dipolar intermediate was... 

A useful compilation of 220 MHz n.m.r. data of substituted bicyclo[3,2,l]octan-6-ones has been published. The bicyclo[3,3,0]octyl cation appears to be implicated in the isomerization of bicyclo[3,2,l]oct-2-ene over SiOj-PaOj at 250 °C as deduced from the scrambling of label in [3- C]-tagged material and the distribution of label in the product, namely bicyclo[3,3,0]oct-2-ene. It has been found that 2,4-diphenyl-bicyclo[3,2,l]octa-2,6-diene (630) and its 6,7-dihydro-derivative undergo base-catalysed hydrogen-deuterium exchange at C-4 at essentially the same rate. Hence, the phenyl groups result in the total elimination of charge delocalization from C-4 to the C-6-C-7 double bond that is found in the unsubstituted bicyclo-octadiene. The... 

The increase in ring size from the norbomadiene-type to bicyclo[2.2.2]octadiene systems appears not to affect the overall reaction outcome. Again the interaction involves... 

It has been suggested307 that the observed thermal rearrangement of the bicyclo[2.2.2]- to the bicyclo[3.2.1]-octadiene skeleton in tricyclic lactams, viz. (265)—>-(266), is consistent with an intramolecular Diels-Alder reaction in which a zwitterion is formed by the migration of one vinyl group from C(l) to C(5) of the lactam moiety (see Scheme 62). It has been shown308 that the 7r-facial selectivity of the Diels-Alder reaction of 1,3-dienes (267) having an attached stereogenic centre can be... 

Shimalactone A 79, a novel polyketide having bicyclo[4.2.0]octadiene and oxabicyclo[2.2.1]heptane units, was isolated from a cultured marine fungus of Emericella variecolor GFIO. Shimalactone A 79 induced neuritogenesis at 10 mg/mL against neuroblastoma Neuro 2A cells. At higher concentration of 20 mg/mL, it showed cytotoxicity against the same cell line. 

Davidiol D (754) isolated from the roots of Sophora davidii was the first natural instance of a resveratrol pentamer [339]. The pentamers amurensins E (751) and F (752) were isolated from the roots of Vitis amurensis Rupr. with an unsaturated benzofuran ring [216]. Upunoside A (753) isolated from the stem of Upuna borneensis (Dipterocarpaceae) is the first instance of a resveratrol pentamer glucoside, and the aglycon has dibenzo-fused bicyclo[5.3.0]octadiene and two dihydrobenzofuran moieties [223], Fig. (45). 

In contrast to norbornadiene, bicyclo[2.2.2]octa-2,5-diene does not always give the transan-nularly bridged products in normal solution reactions, whereas in the anodic electrooxidation this nonconjugated octadiene showed the formation of products, mainly tricyclo-[2.2.2.0 ]octane derivatives 5 and 6 from transannular interaction, exclusively. ... 

Several sesquiterpenes have been synthesized using this methodology. Bicyclo[3.2.1]octadiene 92, obtained in excellent yield from 91, has been used in the synthesis of prezizaene (93). Other targets included sinularene (94) and quadrone (95). ... 

Good routes to semibullvalenes are available from, for example, bicyclo[3.3.0]octadienes, so this rearrangement has been put to use for the produetion of 1,5-disubstituted, and other cyclooctatraenes which are difficult to access (Table 8). It is worth noting in this context that l,2-diazacycloocta-2,4,6,8-tetraene (13) can be made in good yield by the low temperature photolysis of 7,8-diazatetracyclo[3.3.0.0 . 0 ]oct-7-ene (12) (see Section 2.4.1.5.2.8.). 

As noted above, the skeletal rearrangements in the 8, 1 reactions and the stereospecificity in the formation of reaction products are essential criteria of the intermediate formation of nonclassical ions. Nevertheless the results obtained can be explained by assuming the C—J bond ionization to proved with a simultaneous shift of the a-bond C —C in the isomer 350 and of the a-bond C —C in the compound 351. The structures 347 and 348 must be transition states of ionization processes. The authors of , however, consider this assumption less probable because the synchronous process in question is a reaction of the 8, 2 type at the bridged carbon atom and for the bridged atoms of rigid bicyclic systems such processes are known to be strongly hindered. The formation of ion 318 with bicyclo[3,2,I]octadiene skeleton consecutively from ion 347 rather than directly from compound 350 with the geometry of bicyclo[2,2,2]octadiene is also in fuller accordance with the principle of so-called least motion " 29)... 

The reaction of bicyclo[3.1.0]hex-2-ene-c/s-6-carboxaldehyde (118) with the ylide produced from a methyltriphenylphosphonium salt and potassium f-ijutoxide in DMSO produced bicyclo[3.2.1]octadiene (119, equation 11.53). There was evidence for an unstable initial product that rearranged with a rate constant of about 10 s in cyclohexane solution at room temperature to produce the final product. What is the structure of the initial product, and why does it react so rapidly to produce 119 ... 

The cascade process was initially explored with prochiral trienyl iodide 44 (Scheme 16.11) [36, 37]. Mizoroki-Heck cyclization of this precursor produced -ally(palladium species 45, which was trapped by acetate at the least-hindered terminus of the ry -aWyl system to provide CM-bicyclo[3.3.0]octadiene 46 in 60% yield, albeit with very low enantioselectivity (20% ee). Attempts to use silver salts as halide scavengers in this reaction led to the decomposition of 44, presumably resulting from the sensitivity of the cyclopentadienyl moiety. Mizoroki-Heck cyclization of prochiral vinyl triflate 47 with Pd(OAc)2, (S)-BINAP and tetrabutylammonium acetate was more productive, giving diquinane product 48 in excellent yield and 80% ee (Scheme 16.12). The corresponding allylic amine 49 was obtained in analogous fashion using benzylamine as the nucleophile [38]. Allylic acetate 48 was elaborated in seven steps to triquinane /3-ketoester 50, an intermediate in Shibasaki and coworkers [39] earlier total syntheses of ( )-A -capnellene-3/3,8/3,10a-triol (51) and )-A. -c3i me ene-5p, P,l0a,lA-i xdiO (52). 

Asymmetrically induced Heck reactions can also be performed with substrates containing two enantiotopic leaving groups. Starting from dimedone, novel cyclohexa-l,4-diene-l,5-diol bis(nonafluorobutanesulfonates) such as 309 have been prepared and cycUzed under palladium catalysis to cleanly give bicy-clo[4.2.0]octadienes 370 and bicyclo[4.2.0]octenones, respectively, by an unprecedented 4-exo-trig process (Scheme 8.77, cf. Scheme 8.66). In the presence of a chiral phosphine ligand, the products could be obtained with modest enantiomeric excesses (up to 52% ee) [239]. 

Metal-catalysed Isomerizations. The formation of 7r-allylchloropalladium(ii) complexes from a series of cyclopropenes proceeds with symmetrical complexation of the metal to the 7i-bond, and not a-bond cleavage, as the rate-determining step. With substituted cyclopropenes containing a phenyl group at C-3, the it-allyl complex rearranges to indenyl complex either spontaneously or on treatment with triphenyl-phosphine. trans-Chloropalladation of bicyclo[5,l,0]oct-3-ene has been described, and the complex decomposes not to cyclo-octadiene complex, but to a cyclo-octene n-allyl system. ... 

The condensation, reduction, cyclisation and methylation steps shown above result in an a-methoxy-y-pyrone unit appended to a linear polyketide-derived side-chain of varying degrees of reduction. However, the majority of y-pyrone-containing natural products isolated from sacoglossan molluscs do not possess linear side-chains, instead exhibiting complex carbon frameworks commonly characterised by cyclic motifs. For example, 9,10-deoxytridachione (2) [13] possesses a 1,3-cyclohexadiene unit, whilst ocellapyrone A (5) is endowed with a bicyclo[4.2.0]octadiene appendage (Fig. 1.1). 

Like members of the endiandric acid family, ocellapyrone A (5) has a bicyclo[4.2.0]octadiene framework. As such it was hypothesised that 5 is also biosynthesised from a tetraene precursor via an 8k-6k electrocyclisation cascade. To test this hypothesis, Trauner et al. constructed the pyrone-polyene 35 using a StiUe coupling of the pyrone fragment 34 with the stannane 33 [14], The tetraene 35 underwent an 8k-6k electrocyclisation cascade in situ. The product of the initial 8k cychsation, 36, exists as a mixture of exo and endo conformers, with subsequent 6k cychsation of these conformers leading to oceUapyrone A (5) and isomer 37 respectively. The endo product 37 was found to dominate. OceUapyrone B (6) was obtained by exposure of 37 to oxygen (Scheme 1.6). 

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