Mild Ti^III- and Mn/Zr^IV-Catalytic Reductive Coupling of Allylic Halides:  Efficient Synthesis of Symmetric Terpenes

Abstract

Two new efficient methods for the regioselective homocoupling of allylic halides using either catalytic TiIII or the combination Mn/ZrIV catalyst have been developed. The regio- and stereoselectivity of the process proved to increase significantly when the Mn/ZrIV catalyst is used as the coupling reagent and when cyclic substituted allylic halides are used as substrates. The use of Lewis acids such as collidine hydrochloride allowed the quantity of catalyst to be lowered up to 0.05 equiv. We have proved the utility of these protocols with the synthesis of different terpenoids such as (+)-beta-onoceradiene (1), (+)-beta-onocerine (2), squalene (5), and advanced key-intermediates in the syntheses of (+)-cymbodiacetal (3) and dimeric ent-kauranoids as xindongnin M (4a).

Palladium‐Catalyzed Direct Cyclopropylation of Heterocycles

“…Notably,w e identified ap reviously unknown side reaction, wherein the cyclopropyl undergoes an HI elimination/ring opening sequence to give am ixture of trans-a nd cis-1,3-dienes.I n ac ontrol experiment, NaOMe alone did not cause this elimination. [25] Other conceivable organic products such as phenylcyclopropane,p henylcyclopropene,a llylbenzene, and b-methylstyrene were not detected. In terms of the scope with respect to cyclopropyl iodides, various aryl and alkyl groups can be present on the ring (Scheme 2a).…”

Synthesis of New Quaternary Ammonium Salts with a Terpene Function and Evaluation of their Fungicidal and Herbicidal Activities

“…Bromide 2 was prepared by the published method and its 1 H NMR spectrum was found to be identical with the one described. 39…”

“…The starting material in this synthesis was the reactive derivative of limonene -perillyl alcohol (1) which was converted to the bromine derivative 2 using carbon tetrabromide and triphenylphosphine, 39 and to the chlorine derivative 3 using the classic Appel reaction conditions, i.e. carbon tetrachloride and triphenylphosphine in anhydrous DMF.…”

Facile and Efficient Reductive Homocoupling of Benzyl and Aryl Halides Catalyzed by Ionic Liquid [C12mim][CuCl2] in the Presence of Metallic Zinc and Copper

“…However, these above-mentioned protocols, in general, are invariably associated with one or more disadvantages, such as low yields, long reaction times, high reaction temperatures, high catalyst loading, tedious workup procedures, costly metal catalysts, difficulty of catalyst recovery, and environmental toxicity. Reductive coupling reactions using transition metal complexes as catalysts are another important methods for the formation of carbon-carbon bonds, and a variety of reagents, such as palladium [25][26][27][28][29], nickel [30][31][32], iron [33,34], vanadium [35,36], lanthanum [37], zinc [38,39], and other complexes [40][41][42][43][44], have been developed for this conversion. However, most of the procedures still suffered from the use of expensive reagents, difficulties in work up, environmental hazards, and difficulties in recycling of the catalyst.…”