Cyclohexane annulation

For the case of oxyanion, two factors were found to play a role. The size and nature of the ring in which enyne-allene is embedded as well as the steric bulk of the substituents of the allene and alkyne affects the competition between the two cyclizations. The Myers-Saito product is not observed for alkynes with the trimethylsilyl substituent even for cyclohexane-annulated compounds. However, when the alkynyl substituent is changed to phenyl, the resulting relief of steric strain in the C2-C7 transition state permits the cyclization of 25 to occur at low temperature and yields the styrene derivative 26 The cyclopentane-annulated compounds give the Myers-Saito product, or fail to react when a bulky silyl substituent is present at the alkynyl terminus. In contrary, the benzene-annulated compounds undergo rapid the Schmittel cyclization dominantly or exclusively. The cyclizations of oxyanion-substituted enyne-allenes studied in the cited article occured at far lower temperatures than the analogous cyclizations of neutral enyne-allenes. The presence of the oxyanion presumably stabilizes, by resonance, the diradical in the transition state. ... 

Cyclohexane formation is not restricted to 1,6-addition of an allylsilane to a dienone. Equation 10 contains two examples whereby a lengthy tether linking the reactive functionalities leads to cyclohexane annulation via 1,4-conjugate addition. 

At the outset of our investigation, the intramolecular addition of an internal nucleophile to a conjugated dienone was unknown. A cyclohexane annulation via the 1,6-conjugate addition of a lactone enolate to a 3-vinylcyclohexenone derivative was also reported at the first Latest Trends in Organic Synthesis conference held in Blacksburg, Va., May 1984. See M. E. Kraft, R. M. Kennedy and R. A. Holton, Tetrahedron Lett.. 27. 2087 (19861. 

Thermolysis of 3-oxaquadricyclanes in which the bond between Cl and C2 is part of a cyclohexane structure gives a,/J-annulated oxepins 11 in good yield.133 The enlargement of the an-nulated ring favors the arene oxide structure.134... 

The annulation of 4//-thiopyran and cyclohexane rings in 50a results in the planarity of the heterocycle and a half-chair conformation of the carbocycle (81KGS1342). On the other hand, a boat conformation of the 2//-thiopyran ring was found in the crystal of224b [91JCS(P2)2061], Other geometrical parameters were within the limits of the expected values (Fig. 2). 

Lactone 17 was converted to the trans fused octalone 18 by a classical Grignard-type carboannulation. Variations of the organometallic reagent used in the conversion of 17 to 18 and modifications of the substrate and alkylation reagent utilized to produce 15 afford unusually flexible options for the preparation of annulated cyclohexanes. 

This can be achieved only in favorable cases, e.g., by differences in stcric hindrance at both reactive sites in compound 1 or by annulating the epoxide to a cyclohexane chair with locked conformation (principle of diaxial attack4). 

The adamantane structure is unique as it combines three annullated cyclohexane subunits in a nearly spherical overall shape and, as such, it can be regarded as a section of the diamond crystal lattice578. Due to this property, adamantane and other diamondoid molecules are popular as model compounds for synthetic and spectroscopic purposes579 780. 

Under the same photolytic conditions together with Bu3SnH, annulation of the cyclohexane ring can be carried out through the generation of an alkoxyl radical from sulfenate ester (9), 1,5-H shift, nucleophilic addition of the formed carbon-centered radical to methyl vinyl ketone, and finally, treatment with a polar sequence method as shown in eq. 6.6. 

Based on a previously published procedure, it was shown that cyclohexane-1,3-dione reacts with sodium sarcosinate to provide the precursor 233, which could thereafter be efficently annulated to the tetrahydroindole derivative 234 (Equation 73), which should be a useful substrate for further synthetic manipulations <1995SL49>. 

The stereoelectronic preference of sp2 centers in cyclohexane systems for axial attack128 is most probably also found in the peracid epoxidation of methylenecyclohexanes44, where selectivity for axial attack is 0.3 -0.6 keal/mol higher than predicted by the MM2 simulation throughout78. The effect is also detected in derivatives that are substituted in the methylene position, such as isopropylidene derivative 644, and even in annulated derivatives such as 7130 and 5-cholestene81 (see also Tables 3 and 4, Section 4.5.1.1.1.) or the corresponding bicyclic analogs132. 

The ideology of the program layout is similar to that described above for Robinson annulation. Here again it is targeted at the analysis of all cyclohexane fragments present in the target molecule, with the purpose of identifying all... 

Thermolysis of the sodium derivative of the tosylhydrazone (95.1) at 280-340 C gives the fused pyrazole it is possible that a diazo derivative is an intermediate [3292]. The monohydrazone of cyclohexane-1,3-dione is cyclized by heating with ethyl orthoacetate and an acidic catalyst [2565]. Annulation of a hydrazone [such as (95.2)] to a ring-carbon of the original hydrazine may be achieved by heating the compound in DMF with an aryl aldehyde [2912]. 

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