Decalin structure

The olefin metathesis — transannular ene sequence usually provides trans-decalin structure. When (393) was heated at 206 °C in toluene, the ester (396) was isolated, presumably going through the intermediates (394) and (395) 135). 

C. Taillefumier and Y. Chapleur, An entry to enantiomerically pure cts-decalinic structures from carbohydrates, J. Chem. Soc. Chem. Commun. p. 937 (1995). 

The given structure A is confirmed by interpretation of the CH COSY and CH COLOC diagrams. All of the essential bonds of the decalin structure are derived from the correlation signals of the methyl protons. In this, the DEPT subspectra differentiate between the tetrahedral C atoms which... 

For other examples of sluggish Ferrier carbocyclization, see Taillefumier, C, Chapleur, Y, Enantiomerically pure decalinic structures from carbohydrates using intramolecular Diels-Alder and Ferrier carbocyclization. Can. J. Chem., 78, 708-722, 2000. 

The decalin structural feature is contained in steroids, many of which have useful biological activity. Decalin can exist in two isomeric forms depending on whether the rings are trans fused or cis fused, rrans-decalin is constrained to a rigid conformation, whereas cw-decalin is conformationally mobile. 

During the enantioselective synthesis of (3aR,4R,7aS)-4-hydroxy-7a-methylperhydro-1-indenone, a suitable CD-ring fragment for vitamin D-anaiogs, M. Vandewalle et al. realized that the hydroboration/oxidation of (1,1)-ethylenedioxy-8a-methyl-1,2,3,4,6,7,8,8a-octahydronaphtalene led to a c/s-decalin structure instead of the literature reported trans-fusion." ... 

Another reaction that is useful for evaluating the gauche interaction is the transfer of an axial methyl in a [Pg.57]

The given structure A is confirmed by interpretation of the Cff COSY and Cff COLOC diagrams. All of the essential bonds of the decalin structure are derived from the correlation signals of the methyl protons. In this, the DEPT spectra differentiate between the tetrahedral C atoms which are bonded to oxygen (75.5 ppm Cf/—O 72.5 ppm C—O 66.6 ppm C// —O). The methyl protons at J.J9ppm, for example, give correlation maxima with the C atoms at 72.5 59.4 and 44.1 ppm A... 

Formation of cyclic acetals by sugar hydroxyls generally retards nucleophilic displacements at the anomeric centre of the same sugar residue. In the case of 4,6-benzylidene derivatives, the mechanism of deactivation appears to be that the dipole of the C6-06 bond is constrained with its positive end directed towards the anomeric centre.In the case of the 1,2-diketals, the deactivation arises from the increased difficulty of forming half-chair or boat conformations in a six-membered ring, which is part of a traw -fused decalin structure. 

The main disadvantage of the mercuronium ion induced polyene cyclizations is that mostly mixtures of mono-, bi-, tri-, etc. cyclic products are observed. Several examples generating trans-decalin structures via two consecutive 6-endo steps in moderate to useful yields are shown below101 ... 

Two other totally synthetic variants are of interest. Fluvastatin (Lescol) (marketed in 1993) has been shown to lower LDL cholesterol significantly via competitive inhibition of HMG-CoA reductase. Here an indole ring replaces the decalin structure of lovastatin. With the additional phenyl ring it easily supersedes the hydrophobic requirement for the reductase inhibition. The para-fluorine atom undoubtedly enhances potency. Another experimental entry in this effort is RG12561. 

Pravastatin contains a hydroxyl-group at the 6 -position of its decaline structure (Figure 2). This drug was fiist fouitd as a minor urinary metabolite of ML-236B in dogs in 1979. For the industrial hydroxylation of ML-236B, chemical syntheses were initially... 

Intramolecular variants are the most common type of Diels-Alder reactions employed in total syntheses with carbocycles the most popular targets. Among the broad variety of structures in this class, bicyclic decalin structures, both cis and trans, are readily available on intramolecular Diels-Alder reactions. Aube demonstrated the use of a tandem intramolecular Diels-Alder/Schmidt reaction sequence in his synthesis of three stemona alkaloids. The first steps generates cw-decalin intermediate 124, which undergoes a ring expansion in the Schmidt reaction to furnish tricycle 125. ° ... 

For further examples of the Ferrier rearrangement as applied at the start of a synthesis of a thromboxane 62 precursor or of highly oxygenated m-decalinic structures derived from carbohydrates, see Chapter 24. The same reaction applied to the preparation of carbohydrate-based liquid crystals derived from a boronate ester is mentioned in Chapter 17. 

Several tricyclic compounds exist in nature with a cyclopropane ring fused to a cw-decalin structure, as shown in the molecule tricyclo[5.4.0 . 0 ]undecane (below). In various countries, some of these substances have a history of use as folk medicines for purposes such as contraception. Make a model of this compound. How does the cyclopropane ring affect the conformations of the two cyclohexane rings The cyclohexane rings in cw-decalin itself are capable of (simultaneous) chair-chair interconversion (recall Exercise 4-13). Is the same true in tricyclo[5.4.0. 0 ]undecane ... 

The /rara-decalin structure imposes structural rigidity and limits the conformational freedom available to the compound. 

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