Hydrindanes, configuration

After the known intermediate 79 (contaminated with ca. 6 % < /.v isomer) [39] was prepared from Hajos-Parrish ketone [40] 78, the tert-butyl ether was cleaved (quant.) and the ketone protected as the acetal (96 %). The secondary alcohol was oxidized by pyridinium chlorochromate (PCC) to provide ketone 80 in good yield (71 %) and after fractional crystallization afforded material absent of any m-hydrindane (Scheme 10.6). [NOTE All compounds shown in Schemes 10.6 and 10.7 are shown in the ent-configuration, as published]. The oxidation of protected hydrindane 80 under Saegusa-Ito conditions [41, 42] gave enone 81 (82 %), confirmed by X-ray crystallography. 

The fusion of rings of different sizes reduces symmetry in the structures instead of the rather unusual situation with the decalins, where there are only two configurational isomers, the hydrindanes exist in the... 

Standard depictions for steroids, such as those in Scheme 1, overlook the three-dimensional nature of the molecule. The structures in Scheme 2 represent the stereochemical arrangement implicit in the more customary formulas. The junction between rings B and C and also that between rings C and D involve transoid stereochemistry. It is of note in passing that the latter in fact comprises a disfavored trans hydrindane fusion. The ring junction between rings A and B is also transoid but can in selected cases assume a cisoid configuration (2-2). Note further that the stereochemical... 

Chiloschyphone (1) is a sesquiterpene ketone isolated from Chiloscyphus polyanthos and its absolute configuration has not been determined (3). The structure of this compound was first reported in 1972 (4), but later a total synthesis of this compound revealed that this original structure was wrong (5). Quite recently the correct structure was proposed by Connolly and his co-workers to be that depicted as in 1 (3). The synthesis of this correct structure has not been achieved yet. We plan to introduce cw-dimethyl groups by 1,4-addition, followed by an intramolecular aldol cyclization to yield a hydrindane skeleton (Scheme 1). The optical resolution must be possible at the stage of compound 4. 

The hydrindan 23b was later converted by the same group into 26 (Scheme which is a key intermediate in the synthesis of ( )-oppositol and (-)-prepinnaterpene. The conversion involved oxidation of the diene moiety with singlet oxygen and is notable for the clean epimerization of the ring junction to give the trans-configuration (from 25 to 26), which demonstrates that both cis- and trans-junctions can be obtained in the AHR products. 

In the same manner, the configuration of the side chain of hydrindane 215 is established in a 3,3-sigmatropic rearrangement [79]. 

Although the a-orientated isopropyl group should shield the a-face and although the traws-hydrindane generally represents the thermodynamically less stable configuration, compound 66 is formed with high preference. 

D. Since any reaction in which the 0 4 atom takes place in a configuration-ally unstable form (free radical, carbanion, carbonium ion) leads to the stable cis-hydrindan system of rings C and D, the only possibility for obtaining the natural trans-C/D linkage is the use of catalytic hydrogenation. 

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