Twelve- membered

Twelve-membered rings have been obtained using coordination catalysts. The transJmns,ds-cyc. ododec2Lti ien.e has been prepared with a tetrabutyl titanate—diethylalurninum chloride catalyst (48,49) and with a chromium-based system (50). The trans,trans,trans-isom.e-i. has been prepared with a nickel system. 

Moreover, fermentation of various a-substituted cycloalkanone enol esters results in optically active six-, eight-, ten-, and twelve-membered ring ketones with 70—96% ee (84). Isolated enzymes catalyze similar transformations, bacillus coagulans and Candida glindracea]i 2Lse OF (Meito Sangyo) hydrolyze a number of cycHc and acycHc enol esters, giving ketones in 40—80% yield and 14—85% ee (85,86). 

When applying this principle to replacement names generated from fusion nomenclature, it is essential to keep in mind that fusion names for hydrocarbons ending in -cycloalkene are for fully unsaturated skeletons the -ene ending implies whatever number of double bonds may be necessary, without a multiplier. Thus (117) has six double bonds in the twelve-membered ring, and one must add ten hydrogens to saturate it to the stage of a simple benzene derivative, compound (118). 

In the synthesis of the twelve-membered ring, LiC104 was used as a templating ion and the methylbenzo-12-crown-4 (mp 46—48°) was obtained in 15% yield. Alpha-bro-mination was effected in 70% yield and conversion to the bridged species occurred in 20% and 25% yield when n = lor n = 2 respectively. 

The twelve-membered ring SnNH is obtained via the reaction shown in Eq. 6.5. It was characterized by spectroscopic methods (IR, Raman and mass spectra). It is thermally more stable than 6.14 and 6.15, but decomposes to S7NH and Ss after several weeks at 25°C. °... 

The Si-O-B fragment can be formed from different starting materials that generally include chlorosilanes or silanols and boron halides or boric acid derivatives. For the preparation of the cyclic six-, eight-, ten- and twelve-membered borasiloxanes 83-89 four synthetic approaches are known so far, starting from either... 

A similar pre-orientation involving unsaturated carbon chains was operative on generating twelve-membered enediyne 23 and arenediyne lactams 24 [7]. The seco methylesters 21 and 22 were cleaved with LiOH, the corresponding carboxylic acids underwent cyclizations after activation with 2-fluoro-pyridinium tosylate 25 [8]. Dimerization products were found as by-products (<10%). It should be pointed out, that the lactamization succeeded in a single step in about 75% yield by treating the seco-methylesters 21 and 22 with Me3Al in refluxing methylene chloride. Obviously, the latter route was more convenient (Scheme 5). 

Examination of the steric relations in these complexes (cf. Fig. 30) suggests that the more voluminous branched alcohols cannot follow the same principle. Indeed, in the 2-butanol and also in the t-butanol inclusion compound, a different ring system is built (Fig. 17b and type I in Fig. 19). While the short-chain alcohols form twelve-membered H-bond loops, the branched butyl alcohols are embedded into a ten-membered asymmetric loop. The stoichiometry of the asymmetric unit also changes from 1 2 (host guest) ratio to 1 1. The so-built ring system of homodromic H-bonds still contains a mirror-related pair of hosts 1, but comprises only one guest molecule. 

A total synthesis of functionalized 8,14-seco steroids with five- and six-membered D rings has been developed (467). The synthesis is based on the transformation of (S)-carvone into a steroidal AB ring moiety with a side chain at C(9), which allows the creation of a nitrile oxide at this position. The nitrile oxides are coupled with cyclic enones or enol derivatives of 1,3-diketones, and reductive cleavage of the obtained cycloadducts give the desired products. The formation of a twelve-membered ring compound has been reported in the cycloaddition of one of the nitrile oxides with cyclopentenone and as the result of an intramolecular ene reaction, followed by retro-aldol reaction. 

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Finally, it should be pointed out that this twelve-membered ring belongs to the homologous series (R2PN)jj(SN)2 (n=U) and thus the prediction that larger ring sizes may be anticipated in this series has been vindicated. 

A variety of rings of formula CnH S, containing S—S bonds, can be prepared. Several seven-, eight-, nine-, ten-, eleven-, and twelve-membered rings containing 3-8 sulfur atoms, as polysulfide, have been prepared (63) by the reaction ... 

A mixture of sulfanes (H S, n = 3, 4,... n = 6) known as crude sulfane reacts with both SeCl4 and Se Cl in carbon disulfide at low temperatures to form cyclic selenium sulfides of types Se Sg and Se Sj2 - On extraction and recrystallization from carbon disulfide a mixture of twelve-membered ring molecules was obtained as yellow crystals with a selenium content of up to 29 weight-% corresponding to the formula SOj 3. As this sample was much less soluble in CSj than both S,2 and compounds of type Se S8 , it could easily be separated from the latter. The twelve-membered ring molecules have so far been characterized by X-ray crystallography only (see 3.2). 

Weiss and Bachtler have determined the crystal structure of the twelve-membered selenium sulfide. Recrystallization from benzene yields needle-like orthorhombic crystals with the space group Pnnm and unit cell dimensions a = 4.774, b = 9.193, and c = 14.680 A. These values are comparable to the cell parameters of S12 If the crystallization is carried out in carbon disulfide solution and adduct... 

Se Sj2 CS2 and CS crystallize in the trigonal space group R3m. The molecular geometry ot he twelve-membered selenium sulfide ring molecule resembles that of Si2. The structure, however, is also disordered. The distribution of sulfur and selenium over the atomic sites is shown in Fig. 2. 

These peaks are assigned to six- and seven-membered rings (low retention time) and twelve-membered rings (high retention time) since they occur with similar retention times as has been observed for the corresponding homocyclic molecules Sg, S, and... 

Diazocycloalkanones with five- to twelve-membered rings can be synthesized by the present procedure in good yields (Table I).4 Diazo transfer with deformylation can also be used for the preparation of bicyclic a-diazo ketones.10,11 A related procedure involving reaction of the sodium salt of an a-(hydroxy methylene)-ketone with p-toluenesulfonyl azide in ethanol has been applied to the synthesis of diazoalkyl ketones, a-diazo aldehydes, and a-diazo carboxylic esters.12... 

But we succeeded in co-trimerizing butadiene and 2-mono- or 2,3-diaza-dienes to twelve-membered heteroring systems (Fig. 2 in Scheme 2,3-4). Alkylated C=N double bonds react like ethylene with butadiene to 1 2 adducts (Fig. 3, Scheme 2.3-4). Hydrogen-transfer reactions, as mentioned before, are favored in this ca over N-C-bond-forming reactions, so that open-chain instead of heterocyclic products are formed. 

Guella, G. Oztun9, A. Chiasera, G. Mancini, I. Pietra, F. (1997B) Slowly interconverting conformers of twelve-membered, O-bridged, cyclic ethers of red seaweeds in the genus Laurencia. Chem. Eur. J., 3, 1223-31. 

Figure 37 shows the structure of the water complex with the four-armed tetraaza[12]-crown-4 (10). The water molecule is located in the center of the cavity and serves as proton donor to two trans nitrogen atoms. The water molecule also accepts hydrogen bonds from OH side groups attached to the other trans nitrogen atoms. Thus a tetrahedral encapsulation of the water molecule occurs. A remarkable aspect is that the conformation of the twelve-membered ring hardly differs from that of the free ligand (10). 

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