Decalin ring

Decalin ring systems appear as structural units in a large number of naturally occurring substances, particularly the steroids. Cholic acid, for example, a steroid present in bile that promotes digestion, incorporates d5-decalin and rran -decalin units into a rather complex tetracyclic structure. 

Intramolecular Diels-Alder cyclizations of (E)- -nitro-1,7.9-decatrienes under thermal conditions and Lewis acid conditions lead to the formation of decalin ring systems with excellent endo selectivity (Eq. 8.21). This strategy is used for preparing of the AB ring system of norzoanthamine.33... 

Fig. 17 RC/RO ratio of decalin ring-opening on HY zeolites and Pt/HY3 at different conversions. Conversions were varied by changing space time and time on stream. Reaction conditions 2 MPa, 533 K, H2 to feed molar ratio = 65. Adapted from ref. 46.

The common structural feature of quinolizidine alkaloids is a decalin ring system with a nitrogen at one vertex. Often a second or third nitrogen atom is... 

The intramolecular nitrile oxide-alkene cycloaddition has further been used for the construction of a tricyclic isoxazoline intermediate containing a decaline ring. 

U The inside and outside positions of axial substituents in a cis-fused decaline ring are shown in structure 44a. 

Figure 12-22 Representation of c/s-decalin showing nonbonded interactions (shaded areas). The numbering of the decalin ring is the currently accepted convention, which is not the same as the numbering system used generally for bicyclic systems, as described in Section 12-8.

Fig. 4.3 Fi rst generation statins having substituted decalin rings.

The research teams of Merck, Sharpe and Dohme (USA) were the first to succeed in finding a synthetic statin analogue that contained a biphenyl moiety [2] instead of a decalin ring (Fig. 4.4). 

Ohloff G. Relationship between odor sensation and stereochemistry of decalin ring compounds. In Gustation and Olfaction. 1971. Ohloff G, Thomas AF, eds. Academic Press, London, pp. I78-I83. Bersuker IB,DimogIo AS, Gorbachov MY, Koltsa M, Vlad PE. New J. Chem. I985 9 2II. 

A jS-phenethylamine moiety was incorporated into the trans-decalin ring system (45)... 

While it is not clear from these applications whether the Wharton reaction necessarily proceeds via trans diaxial epoxide opening, Ziegler et al in synthetic studies towards quassinoids, have found that there is no such stereoelectronic requirement in a rigid fraws-decalin ring system (Scheme 16). 

The oxygen bridge in oxabicyclic compounds is an electron pair donor that can stabilize a-carbocations. This characteristic renders oxabicyclic substrates more susceptible to carbocationic skeletal rearrangements resulting in the cleavage of the carbon framework. One such reaction was exploited by Sammes for the synthesis of ( )-cryptofauronol, in which treatment of 145 with Lewis acid induces rearrangement to a decalin ring system, Eq. 100 [57]. 

The feasibility of cyclizing polyenes with iminium ion initiators has received only scant attention. 72 Cyclization of imine (77) under aprotic conditions with SnCU affords predominantly rran -decalins containing endocyclic unsaturation. This mixture was deduced by H NMR analysis to contain diastereomers (78) to (81) in the indicated abundances as depicted in equation (7). The extent of asymmetric induction in forming the decalin ring system (9S,10iS 9/ ,10/ = 61 39) is significantly lower than that of related cyclizations of chiral acetal substrates. ... 

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