Total syntheses of oridamycin A, triptoquinones B and C and isoiresin are accomplished from a common intermediate prepared via iridium catalyzed alcohol C-H tert-(hydroxy)-prenylation; a byproduct-free process that forms an all-carbon quaternary stereocenter with excellent control of diastereo- and enantioselectivity.

Steroids have long been sought after as synthetic targets. Their rearranged counterparts, though, have only recently received more attention, when isolation and biological testing programs revealed several molecular entities that were both structurally intriguing as well as biologically relevant. This review will highlight contemporary synthetic approaches towards the growing class of seco- and abeo-steroids and some related triterpenoid natural products.1 Introduction2 Cyclocitrinol2.1 Li’s Synthesis of Cyclocitrinol2.2 Gui’s Synthesis of Cyclocitrinol3 Strophasterol3.1 Heretsch’s Synthesis of Strophasterol A3.2 Kuwahara’s Synthesis of Strophasterols A and B4 Pleurocin A/Matsutakone and Pleurocin B4.1 Heretsch’s Synthesis of Pleurocin A/Matsutakone and Pleurocin B5 Aplysiasecosterol A5.1 Li’s Synthesis of Aplysiasecosterol A6 Glaucogenins C and D6.1 Tian’s Syntheses of 5,6-Dihydro-glaucogenin C and Glaucogenin D7 Physalin B7.1 Sodeoka’s Synthesis of the DFGH Ring System of Physalin B8 Limonin8.1 Hirama’s Synthesis of (±)-Limonin9 Schiglautone A9.1 Ding’s Synthesis of (±)-atrop-Schiglautone A10 Conclusion

The synthesis of 2,4,6-triphenylphosphinine has been revisited and a general protocol for the preparation of such low-coordinate phosphorus compounds in good to excellent yields could be established. This allows to investigate several aspects of the chemistry of 2,4,6-triarylphosphinine, such as the reaction with in situ generated benzyne to give 2,4,6-triphenylphosphabarrelene. The corresponding 2,4,6-triphenylphosphabarrelene-selenide could be characterized crystallographically for the first time and the structural and electronic properties of this cage-compound in comparison to classical triarylphosphines could be evaluated. Moreover, [(L)W(CO)5)] complexes of both 2,4,6-triphenylphosphinine and 2,4,6-triphenylphosphabarrelene were prepared and characterized by means of X-ray crystallography. This allowed for the first time a direct structural comparison of these related phosphorus compounds, coordinated to the same metal fragment.

Benzilic acid rearrangement of i-steroid ketones and their subsequent opening gives access to 5(6→7)abeo-steroids. The functional group tolerance is demonstrated by several examples, including substrates with additional olefinic groups. The method opens a potential route to the synthesis of complex natural products such as solanioic acid from abundant steroid starting materials like ergosterol.

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