Cis Selective RCM Study to the 14-Membered Cyclic Subunit of Bielschowskysin

A concise, (Z)-selective ring-closing metathesis (RCM) route to the 14-membered carbocycle of bielschowskysin is detailed using naturally occurring chiral starting materials. Unproductive RCM substrates were attributed to alkyne chelation of the ruthenium catalyst and steric disadvantages within the cembranoid precursors, which was eventually circumvented by using cyclic diol benzylidene protection involving a C8-quaternary carbinol center.

A Catalytic Approach for Enantioselective Synthesis of Homoallylic Alcohols Bearing a Z-Alkenyl Chloride or Trifluoromethyl Group. A Concise and Protecting Group-Free Synthesis of Mycothiazole

A protecting group-free strategy is presented for diastereo- and enantioselective routes that can be used to prepare a wide variety of Z-homoallylic alcohols with significantly higher efficiency than is otherwise feasible. The approach entails the merger of several catalytic processes and is expected to facilitate the preparation of bioactive organic molecules. More specifically, Z-chloro-substituted allylic pinacolatoboronate is first obtained through stereoretentive cross-metathesis between Z-crotyl-B(pin) (pin = pinacolato) and Z-dichloroethene, both of which are commercially available. The organoboron compound may be used in the central transformation of the entire approach, an α- and enantioselective addition to an aldehyde, catalyzed by a proton-activated, chiral aminophenol-boryl catalyst. Catalytic cross-coupling can then furnish the desired Z-homoallylic alcohol in high enantiomeric purity. The olefin metathesis step can be carried out with substrates and a Mo-based complex that can be purchased. The aminophenol compound that is needed for the second catalytic step can be prepared in multigram quantities from inexpensive starting materials. A significant assortment of homoallylic alcohols bearing a Z-F₃C-substituted alkene can also be prepared with similar high efficiency and regio-, diastereo-, and enantioselectivity. What is more, trisubstituted Z-alkenyl chloride moiety can be accessed with similar efficiency albeit with somewhat lower α-selectivity and enantioselectivity. The general utility of the approach is underscored by a succinct, protecting group-free, and enantioselective total synthesis of mycothiazole, a naturally occurring anticancer agent through a sequence that contains a longest linear sequence of nine steps (12 steps total), seven of which are catalytic, generating mycothiazole in 14.5% overall yield.

Regioselective formation of 1,1-disubstituted allenylsilanes via cross-coupling reactions of 3-tri-n-butylstannyl-1-trimethylsilyl-1-propyne

The regioselective Stille cross-coupling reactions of 3-tri-n-butylstannyl-1-trimethylsilyl-1-propyne demonstrate isomerization following the initial transmetalation step resulting in allenyl palladium intermediates for reductive coupling to yield conjugated 1,1-disubstituted allenylsilanes.

Expedient Synthesis of (±)-Bipinnatin J

[reaction: see text] A nine-step, stereoselective synthesis of bipinnatin J is described, which features a ruthenium-catalyzed Alder-ene reaction, a Stille cross coupling, and an intramolecular Nozaki-Hiyama-Kishi allylation as key steps. The biosynthetic relationship between bipinnatin J and complex polycyclic diterpenes isolated from gorgonian corals is discussed.

Synthetic studies towards furanocembrane diterpenes. A total synthesis of bis-deoxylophotoxin

Synthetic approaches to the furanocembrane family of natural products, e.g. lophotoxins, pukalides, bipinnatins, based on: i) an intramolecular cyclisation of an alpha,beta-unsaturated acyl radical intermediate into a conjugated enone, and ii) an intramolecular Stille coupling reaction involving a 2-stannylfuran and a vinyl iodide, are described. A total synthesis of bis-deoxylophotoxin , the probable biological precursor to the neurotoxin lophotoxin, isolated from species of the Pacific sea whip Lophogorgia, is then presented.