Enantioselective Total Synthesis of a trans‐Hydrindane Rings/Side‐Chain Building‐Block of Vitamin D − Asymmetric Induction in an Acid‐Catalyzed Conjugate‐Addition Reaction

Abstract

For the enantioselective total synthesis of 1α,25‐dihydroxyvitamin D3 (3), we have developed an enantioselective approach to the “northern” portion building‐block 8, starting from the optically active hexanoic acid derivative 44, 2‐methylcyclopent‐2‐en‐1‐one (10) and 1‐(phenylthio)but‐3‐en‐2‐one (9). The steric course of the addition reaction of homochiral (S)‐ketene acetals 28, 40, 44 and 58 with 10 was examined. We found that in the cases of 28, 44 and 40, the reactions occur with high simple and induced (facial) diastereoselectivities. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Methodology for the Construction of the Bicyclo[4.3.0]nonane Core

“…Similarly, utilization of cyclopentanone 176 with ketone 177 led to formation of hydrindene 178 in 78% [102]. Other examples have appeared in the literature [103][104][105][106]. In a similar vein as the Michael additions, the Morita-Bayliss-Hillman under phosphine or transition metal catalysis has been shown to provide similar results to Michael addition strategies (see Scheme 26).…”

“…Similarly, utilization of cyclopentanone 176 with ketone 177 led to formation of hydrindene 178 in 78% [102]. Other examples have appeared in the literature [103][104][105][106].…”

Structural revision and pharmacological activity of hemslecin C

“…1 Natural products provide various skeletons and exhibit diverse biological activities, their chemical constituents are determined and often modified by researchers to obtain more effective drugs. 2,3 Hemsleya is a traditional Chinese medicinal plant which has the biological activities of detoxification and antiinflammatory sterilization, 4,5 and it has traditionally been used for treating hepatitis, coronary heart disease, tracheitis, and sore throat. 6 Hemslecin A (Figure 1), a cucurbitane-type tetracyclic triterpenoid, mainly exists in the rhizomes of Hemsleya, a cucurbitaceous plant.…”

A Concise Account of Various Approaches for Stereoselective Construction of the C-20(H) Stereogenic Center in Steroid Side Chain

“…Comparatively, little attention was paid to the side chain except for two carbon units present in corticosteroids and other pregnane derivatives and interconversions between the side chains of cholesterol, plant sterols, and bile acids. The last few decades have witnessed intensive research on side-chain synthesis, yielded many imaginative syntheses of general interest, and contributed to a great extent to the development of stereospecific chiral carbon formation. , The biological significance of both the C-20 epimers of naturally occurring and/or synthetic sterol molecules provided not only steroid chemists but also natural product chemists an opportunity to pursue new syntheses of sterols or compounds with similar chain structures. This review is limited to sequences commencing upon generation of both epimers at C-20.…”