New strategy for convergent steroid synthesis

A stereospecific total synthesis of DL-hexahydroapoerysopine

A stereospecific total synthesis of DL-hexahydroapoerysopine, an intriguing and historically important Apo rearrangement product of the aromatic Erythrina alkaloids bearing the all-cis ring fusion stereochemistry, was achieved via an efficient acid-mediated stereospecific skeletal rearrangement.

From an ent-Estrane, through a nat-Androstane, to the Total Synthesis of the Marine-Derived Δ8,9-Pregnene (+)-03219A

The total synthesis of (+)-03219A, a rare Δ^8,9-pregnene isolated from the marine-derived Streptomyces sp. SCSIO 03219, is described that is based on a series of transformations that enable progression from epichlorohydrin to an ent-estrane, then conversion to a nat-androstane, and finally establishment of the natural product target. Key to the success of these studies was implementation of two rearrangement processes to formally invert the quaternary center at C13 and establish the C10 quaternary center.

A review on various aspects of organic synthesis using Comins' reagent

Recently, researchers have shown great interest in compounds such as triflate and enotriflate that are synthesized by Comins reagent. For the above-mentioned reason, we planned to review the works related to organic synthesis using Comins reagent. So this review includes a whole new investigation of the Comins reagent which is used for stereoselective conversion of α-keto ester, enolate to enol triflate of lactone and vinyl triflate to methyl ketone. Comins reagent plays an important role in regioselectivity such as transformations of ketone or dienolates into vinyl triflates and it has a major application in highly selective oxidation in an easy and environmentally friendly manner.

Iridium-catalyzed α-alkynylation of cyclic nonaromatic eneformamides: application to the synthesis of azapolycyclic architectures

A regioselective and chelation-assisted dehydrogenative alkynylation of cyclic nonaromatic eneformamides with terminal alkynes, under iridium catalysis, is described.

Mechanistic Studies of the Deslongchamps Annulation

The Cs₂CO₃-mediated annulations ("Deslongchamps annulations") of three spirocyclic benzoquinone monoketals 5b-d with an ester or acyl substituent at C-2 to two tert-butyl esters of γ,δ-unsaturated β-ketocarboxyl acids ("Nazarov reagents"; 2a,b) were monitored ¹H NMR spectroscopically. This revealed that a primary product, by all likelihood the Michael adduct, forms fast and prior to the appearance of the Deslongchamps adduct. These primary products form reversibly. This was proved by two crossover and four scavenging experiments. Therein, components already incorporated in one of the mentioned primary products ended up in Deslongchamps adducts different from the one, which would have resulted if the respective primary product had reacted alone. However, these experiments leave open whether our primary products are intermediates en route to Deslongchamps products or whether they represent dead ends.

A hybrid approach to new molecular scaffolds

Our various efforts toward the synthesis of a set of novel sugar hybrid scaffolds of several biologically active natural products such as taxol, steroids, β-lactams, and otteliones are presented. We have shown the application of the hybrid approach to design and rapidly generate a library of novel natural product-like compounds, which may have interesting biological features, using metathesis and/or cycloaddition reactions as key steps.

Deslongchamps annulations with benzoquinone monoketals

The so-called Deslongchamps annulation of deprotonated γ,δ-unsaturated β-ketoesters 15 to 2-(alkoxycarbonyl)cyclohex-2-en-1-ones or similarly activated cyclohex-2-en-1-ones offers a versatile access to various kinds of decalindiones. The scope of Deslongchamps annulations was extended by establishing acceptor-substituted benzoquinone monoketals such as 13 as viable substrates. They gave octalindiones such as 35 with diastereoselectivities ≥ 95:5.

Synthetic Studies toward Highly Functionalized 5β-Lanosterol Derivatives: A Versatile Approach Utilizing Anionic Cycloaddition

Stereoselective synthesis of the potentially biologically valuable 5beta-lanosteroidal-type backbone was achieved via anionic cycloaddition. Synthesis of the two new bicyclic Nazarov intermediates 14 and 40 and their cycloaddition with chiral cyclohexenone 25 and further functional group manipulations resulted in highly functionalized tetracyclic intermediates 28 and 44. These synthetic intermediates could lead to the total synthesis of new lanosterol-based inhibitors.

Design and synthesis of novel sugar-oxasteroid-quinone hybrids

A new class of sugar-oxasteroid-quinone hybrid molecules has been designed and synthesized involving an efficient enyne metathesis/Diels-Alder reaction strategy.

Steroids: reactions and partial synthesis

This article reviews the progress in the chemistry of the steroids that was published between January and December 2003. The reactions and partial synthesis of estrogens, androgens, pregnanes, cholic acid derivatives, cholestanes and vitamin D analogues are covered. There are 152 references.

Cascade polycyclization: exploration of a convergent route to access various tricyclic and tetracyclic products related to sterols

The expedient synthesis of tricyclic and tetracyclic compounds via a cascade polycyclization methodology is described. Nazarov substrates (II) containing two Michael acceptors and a cyclohexenone ester (I) underwent cycloaddition followed by intramolecular 1,4-addition to furnish, in a highly stereoselective manner, tricyclic and tetracyclic products (III). Such compounds are interesting intermediates for the synthesis of polycyclic natural and unnatural products.