Cyclization cyclooctene

Tetrahydrobis(benzofuran) is produced by a tandem cyclization reaction from the bis-vinyl ether on reaction with catalytic quantities of rhodium(l) salts in the presence of electron-rich phosphine ligands <20030L1301>. Thus, employing 10mol% of [RhCl(coe)2]2 with 20mol% of a dicyclohexyl ferrocenyl phosphine ligand produces the bis-cyclized product (coe = cyclooctene Equation 67). 

Stereoselective radical cyclization of 1,5-cyclooctadienes. Winkler and Sridar14 have noted transannular effects on the stereochemistry of cyclization of these octadienes (equation I). Thus radical cyclization of cis-1 and of the corresponding ketone (3) is highly frans-selective and is more rrans-selective than that of the monosubstituted diene 5. Cyclization of a 3,8-disubstituted cyclooctene is... 

One of the most popular methods for creating the anatoxin-a skeleton is by transannular cyclization of a suitably substituted cyclooctene. This approach was used in the first synthesis of racemic anatoxin-a (Campbell et al. 1979). They carried out two different methodologies in order to reach the 9-azabicyclo[4.2.1]nonane structure (Scheme 7.3). The 1,5-cyclooctadiene (10) starting compound was transformed into the methyl amine 11 which was treated with hypobromous acid to produce the desired bicycle 12 as a mixture of diastereoisomers in 29% overall yield, with some amount of the azabicyclo[3.2.1] analogue (Bastable etal. 1972). 

The syn addition of iodine azide has been observed with a strained cyclobutene derivative29. Anomalous products were obtained from (i )-cyclooctenes and bicyclic (-E -cyclooctenes30,3I, e.g., 5-7. From 1,5-cyclononadiene and 1,5- and 1,6-cyclodecadiene, stereoselective transannu-lar cyclization occurred, involving acetonitrile (solvent) as the nucleophile to give 8--1032. From 1,3-dienes, benzofuran and A-acylindoles were obtained 1,2- or 1,4-diazides via the corresponding iodo azides (Section 7.2.2.4.). 

Pyrrolizidines 1 were obtained with high stereocontrol (100% tram addition) by intramolecular cyclization of l-aza-4-cyclooctene with phenylsulfenyl or phenylselenenyl halides. Analogous results were also obtained by the mercury-induced cyclization performed with mercury(II) chloride in tetrahydrofuran113. 

Bromine and iodine were both effective for the cyclization of l-aza-4-cyclooctene to the corresponding pyrrolizidine 3 which is obtained in good yield without conflicting amine oxidation. The cyclization of l-aza-5-cyclonene and of cyclophenylalkanamines was similarly performed (Table 6) 3-121 23>, The total stereoselectivity is dependent on either the strain connected with the polycyclic system or the tram addition to the double bond. The stereochemistry of the products was confirmed by X-ray analysis. 

Thiiranium ions were proposed as intermediates in acid-catalyzed sulfur-atom transfer from sultene 29 to cyclic olefins under thermal conditions (Scheme 45). A high degree of diastereospecificity was observed during the sulfur atom transfer reaction to /ra r-cyclooctene. S-Dealkylation is facilitated by the formation of a stablilized carbocation, which may further cyclize or rearrange <1998JA4861>. Similar sulfur-atom transfer to cyclooctyne afforded a relatively stable thiirenium salt that did not undergo S-dealkylation (Section 1.06.5.2) <2002JA8316>. 

Adam, W., Stegmann, V. R. Unusual Temperature Dependence in the cis/trans-Oxetane Formation Discloses Competitive Syn versus Anti Attack for the Patemo-Buchi Reaction of Triplet-Excited Ketones with cis- and trans-Cyclooctenes. Conformational Control of Diastereoselectivity in the Cyclization and Cleavage of Preoxetane Diradicals. J. Am. Chem. Soc. 2002,124, 3600-3607. 

An exception to this generalization has been noted for E- and Z-cyclooctene. This reaction is nearly stereospecific at low temperature. This result is attributed to conformationally distinct 1,4-diradical intermediates that undergo intersystem crossing and cyclization faster than stereochemical interconversion. 

Formation of a trans-cyclooctene system reveals a profound stereochemical effect of the metathesis (using either 1 or the Schrock catalyst). The other diastereoisomer does not undergo cyclization. 

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