Brominative cyclizations of geranyl derivatives

One-Electron Oxidation of Geranyl Acetone Derivatives Using Ceric(IV) Ammonium Nitrate and Manganese(III) Acetate: Carbon–Carbon Bond Formation

Oxidation of geranyl acetone derivatives with ceric ammonium nitrate (CAN) and Mn(OAc)3 afforded tricyclic and bicyclic compounds as well as hydroxy and nitro compounds as a result of one-electron oxidation followed by carbon–carbon bond formation. This is the first example of radical cyclization (formed by one-electron oxidation) of geranyl acetone derivative 1 and its isomer 4 to give tri- and bicyclic products with carbon–carbon bond formation.

Chemistry of the Secondary Metabolites of Termites

Isolation, structure determination, synthesis, and biochemistry of the low-molecular-weight compounds of the secretion of exocrine glands of termites are described, with an emphasis on pheromones and defensive compounds.

NXS, Morpholine, and HFIP: The Ideal Combination for Biomimetic Haliranium-Induced Polyene Cyclizations

In contrast to Nature that accomplishes polyene cyclizations seemingly with ease, such transformations are difficult to conduct in the lab. In our program dealing with the development of selective halogenations of alkenes, we now asserted that standard X⁺ reagents are perfectly suited for the biomimetic cation-π cyclization of both electron rich and poor linear polyenes in the presence of the Lewis base morpholine and the Lewis acid HFIP. The method stands out due to its broad substrate scope and practicability together with high chemical yields and excellent selectivities, even for highly challenging chloriranium-induced polyene cyclizations.

Stereoselective Halogenation in Natural Product Synthesis

At last count, nearly 5000 halogenated natural products have been discovered. In approximately half of these compounds, the carbon atom to which the halogen is bound is sp(3) -hybridized; therefore, there are an enormous number of natural products for which stereocontrolled halogenation must be a critical component of any synthesis strategy. In this Review, we critically discuss the methods and strategies used for stereoselective introduction of halogen atoms in the context of natural product synthesis. Using the successes of the past, we also attempt to identify gaps in our synthesis technology that would aid the synthesis of halogenated natural products, as well as existing methods that have not yet seen application in complex molecule synthesis. The chemistry described herein demonstrates yet again how natural products continue to provide the inspiration for critical advances in chemical synthesis.

Accessing Brominated Natural Product Motifs Using Phosphoramidite Catalysis

This article describes the application of a first-generation phosphoramidite catalyst to the construction of the most commonly encountered subunits of bromine-containing natural products. The process is compared with previous efforts, and is found to be complementary to existing methods. Application of the process enables bromocarbocyclisations, bromoetherifications, and bromoallene formation using the common laboratory reagent N-bromosuccinimide.

Oxidative oxygen-nucleophilic bromo-cyclization of alkenyl carbonyl compounds without organic wastes using alkali metal reagents in green solvent

A bromo-lactonization of alkenyl carboxylic acids and a bromo-cyclization ofN-allyl amides as oxygen-nucleophilic bromo-cyclization reactions were developedviathe oxidative umpolung of bromide using alkali metal bromide and inorganic oxidant.

A short asymmetric route to the bromophycolide A and D skeleton

An asymmetric synthesis of the bromophycolide D ring system has been achieved in seven steps from a known geranylgeranylated benzoate, via bromonium-promoted transannular cyclization of a macrocyclic intermediate.

Simple reagents for direct halonium-induced polyene cyclizations

Although there are many reagent combinations that can initiate polyene cyclizations, simple electrophilic halogen sources have not yet proven broadly effective as promoters of such processes. Herein is described a readily prepared and stable class of reagents capable of effecting such transformations for a wide range of electron-rich and -deficient terpenes derived from geraniol, farnesol, and nerol, thereby enabling the effective synthesis of a diverse array of complex chlorine-, bromine-, and iodine-containing polycyclic frameworks. Efforts to date have led to the first racemic laboratory total synthesis and structural revision of the anti-HIV natural product peyssonol A as well as an efficient and concise inaugural total synthesis of peyssonoic acid A. They have also permitted formal racemic total syntheses of aplysin-20, loliolide, K-76, and stemodin to be achieved through routes that are typically shorter, higher-yielding, and more environmentally conscious than previous efforts. Preliminary attempts to use chiral forms of the reagent class for enantioselective alkene halogenation are also described.

Synthesis and bioassay of isoprenoid 3-alkylthio-1,1,1-trifluoro-2-propanones: potent, selective inhibitors of juvenile hormone esterase

Four 3-alkylthio-1,1,1-trifluoro-2-propanones with juvenile hormone-like side chains were prepared from citronellol and homogeraniol. These substrates were designed as possible transition-state analogs for the juvenile hormone (JH)-specific esterases present in insects. These four isoprenoid trifluormethyl ketones were assayed in vitro with JH esterase and general esterases from larvae of the cabbage looper, Trichoplusia ni (Lepidoptera, Noctuidae), and with eel acetylcholinesterase and bovine chymotrypsin. JH esterase inhibition I50 values were in the nanomolar range for all four compounds, while the other esterases had I50's which were 10(3) to 10(5) higher. The high selectivity of these inhibitors is believed to be due to their similarity in size and functionality to natural JH III. Treatment of T. ni larvae in vivo with solutions of the most active analog, 3-[(E)-4,8-dimethyl-3,7-nonadienylthio]-1,1,1-trifluoro-2-propanon e (DNTFP) causes a dose-dependent delay in pupation and a concurrent selective inhibition of JH esterase. These data support the hypothesis that the reduction in in vivo JH titer in larval T. ni is due, in part, to hydrolysis of the hormone by selective esterases. DNTFP appears to be competing with JH for the active site of JH esterase.