Ten membered ring

Ten-membered Rings.—n.m.r. spectroscopy shows that 1,1-difluorocyclo-decane prefers the predicted boat-chair-boat conformation, and various possible routes for ring inversion are discussed.3,3-Difluoro-trans-cyclodecene adopts at least five of eight possible conformations at — 152 °C, and four of 

Borgen, J. Dale, and. 1. Schaug. Acta Chem. Scand., 1972, 26, 1073. 

The failure of cw,cw-cycIodeca-l,6-diene to polymerize has been discussed earlier (Section 12.3.1). In conjunction with WCle it is said to catalyze the polymerization of c/s,cjs-cycloocta-l,5-diene and of cyclododecene at 20°C (Kupper 1979). 

Cyclodecane-l,6-dione has been found to have a dipole moment of 0.7 A short review of the determination of conformations of the germacrene type of sesquiterpenes using nuclear Overhauser effects and the influence of these conformations on Cope rearrangements in these systems, has been published. 

The conformation of confertolide (13) has been established by a study of nuclear Overhauser effects.  

Larger Rings.—Cycloundecanone was shown, by an X-ray structure determination carried out at 108 K to have the triangular conformation (14). Bond distances and angles are fairly normal.  

Toubiana, M.-J. Toubiana, K. Tori, and K. Kuriyama, Tetrahedron Letters, 1974, 1753. 

spectrum of cis,cis-cyclododeca-l,3-diene is compatible with the molecule adopting a slightly twisted, transoid conformation, whereas the u.v. spectra of cis,trans-and trans,trfl js-cyclododeca-l,3-diene indicate almost planar transoid conformations. The last-named is the smallest conjugated trans,trans cyclic diene yet characterized.  

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Beginning in the 1980s research directed toward the isolation of new drugs derived from natural sources identified a family of tumor inhibitory antibiotic substances characterized by novel struc tures containing a C C—C=C—C C unit as part of a nine or ten membered ring With one double bond and two triple bonds (-ene + di- + -yne) these com pounds soon became known as enediyne antibiotics The simplest member of the class is dynemian A most of the other enediynes have even more compli cated structures... 

Enediyne antibiotics (Section 9.4) A family of tumor-inhibiting substances that is characterized by the presence of a C=C—C=C—C = C unit as part of a nine- or ten-membered ring. 

Perhaps the most notable difference between S-N and N-O compounds is the existence of a wide range of cyclic compounds for the former. As indicated by the examples illustrated below, these range from four- to ten-membered ring systems and include cations and anions as well as neutral systems (1.14-1.18) (Sections 5.2-5.4). Interestingly, the most stable systems conform to the well known Htickel (4n -1- 2) r-electron rule. By using a simple electron-counting procedure (each S atom contributes two electrons and each N atom provides one electron to the r-system in these planar rings) it can be seen that stable entities include species with n = 1, 2 and 3. 

Of great importance for the Bergman cyclization is the distance between the triple bonds. The reaction cannot occur at moderate temperatures if the distance is too large. Optimal reactivity at physiological temperatures is obtained by fitting the enediyne element into a ten-membered ring." ... 

In this beautiful synthesis of periplanone B, Still demonstrated a classical aspect and use of total synthesis - the unambiguous establishment of the structure of a natural product. More impressively, he demonstrated the usefulness of the anionic oxy-Cope rearrangement in the construction of ten-membered rings and the feasibility of exploiting conformational preferences of these medium-sized rings to direct the stereochemical course of chemical reactions on such templates. 

The total synthesis of biotin (1) described in this chapter provides an impressive example of the intramolecular nitrone-olefin [3+2] cycloaddition reaction. Aiming for a practical process, the Hoff-mann-La Roche group utilized relatively simple and inexpensive starting materials, and ingeniously controlled the crucial [3+2] cycloaddition reaction to give only one stereoisomer by confining the cycloaddition precursor to a ten-membered ring. 

The dichloro derivative 4, together with the ten-membered ring compound 5, is formed from the dilithio compound 3 by successive treatment with sulfur and sulfur dichloride.413... 

In analogy to Edstrom s experiments, the nine- and ten- membered ring lactams underwent regio and stereoselective transannular ring contractions to give the corresponding indolizidinones and quinolizidinones, respectively (vide supra Scheme 56) (Table 21) [61]. 

Besides these intermolecular adducts an example for an intramolecular adduct has recently been reported. Thus, a ten-membered ring 78, which contains two stannylene units, has been synthesized 101) (Eq. (35)). 

Each of these tin atoms acts as a Lewis acid, with two neighboring nitrogen atoms functioning as electron donors. The ten-membered ring folds up to generate a four-membered cycle bridged at the 1,3- and 2,4-positions. The structure, which can easily be deduced from high-resolution NMR spectra, is displayed in Fig. 14. 

The problem of the preferred conformation of cyclodecane has been extensively studied by Dunitz et al. (46). In the crystals of seven simple cyclodecane derivatives (mono- or 1,6-disubstituted cyclodecanes) the same conformation was found for the ten-membered ring (BCB-conformation, Fig. 9). It follows from this that the BCB-conformation is an energetically favourable conformation, possibly the most favourable one. Numerous force field calculations support this interpretation Of all calculated conformations BOB corresponded to the lowest potential energy minimum. Lately this picture has become more complicated, however. A recent force field calculation of Schleyer etal. (21) yielded for a conformation termed TCCC a potential energy lower by 0.6 kcal mole-1 than for BCB. (Fig. 9 T stands for twisted TCCC is a C2h-symmetric crown-conformation which can be derived from rrans-decalin by breaking the central CC-bond and keeping the symmetry.) A force field of... 

The six- and seven-membered rings S5NR and S6NR are yellow oils that exhibit molecular ions in their electron-impact mass spectra. The nine- and ten-membered rings S8NH and S9NH form photosensitive, pale yellow crystals that are soluble in CS2. The 12-membered ring SnNH has only been characterized by spectroscopic methods.207... 

This ring contraction has been used to provide the ten-membered ring of the germacranolide aristolactone (4) from a 13-membered allylic propargylic ether. 

Vinylketene complexes, generated by treatment of heteroatom-substituted carbene complexes with alkynes, can react intramolecularly with different nucleophiles to yield cyclic compounds (Figure 2.30, Table 2.20). Four- to ten-membered rings have... 

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