Helena M. C. Ferraz

(+)- and (−)-Mutisianthol: First Total Synthesis, Absolute Configuration, and Antitumor Activity†

The first synthesis of the natural product (+)-mutisianthol was accomplished in 11 steps and in 21% overall yield from 2-methylanisole. The synthesis of its enantiomer was also performed in a similar overall yield. The absolute configuration of the sesquiterpene (+)-mutisianthol was assigned as (1S,3R). Key steps in the route are the asymmetric hydrogenation of a nonfunctionalized olefin using chiral iridium catalysts and the ring contraction of 1,2-dihydronaphthalenes using thallium(III) or iodine(III). The target molecules show moderate activity against the human tumor cell lines SF-295, HCT-8, and MDA-MB-435.

Synthesis of N-substituted pyrrole and tetrahydroindole derivatives from alkenyl β-dicarbonyl compounds

Abstract The iodocyclization of a series of alkenyl-substituted β-enamino esters and ketones, followed by base-promoted dehydroiodination, led to the formation of the corresponding pyrrole or tetrahydroindole derivatives. In the absence of base, the iodo-β-enamino esters 5 and 7 underwent spontaneous aromatization after dehydroiodination, furnishing the 4, 5, 6, 7-N-substituted-tetrahydroindoles 19 and 20 . All the elimination reactions proceeded smoothly, in yields ranging from 71% to 99%. Starting from the β-allyl-dimedone 21 , it was possible to prepare the oxotetrahydroindole 24 , in moderate overall yield.

Preparações e aplicações sintéticas recentes de enaminonas

Enaminones are b-enamino carbonylic compounds bearing the conjugated system N-C=C-C=O, which makes them versatile ambident synthetic building blocks, particularly in synthesis of heterocycles. This review covers the last three years of the literature concerning the preparation and synthetic applications of enaminones.

Natural occurrence, biological activities and synthesis of eight-, nine-, and eleven-membered ring lactones

The natural occurrence, biological activities and synthetic approaches to natural eight-, nine-, and eleven-membered lactones is reviewed. These medium ring lactones are grouped according to ring size, and their syntheses are discussed. The structures of some natural products early identified as medium-ring lactones were revised after total synthesis.

The stereoselective synthesis of terpene tetrahydrofurans using thallium triacetate

Abstract The reaction of diterpenes 1–3 and monoterpenes 9 , 10 with thallium triacetate leads stereoselectively to the tetrahydrofuran products 5–7 and 11 , 12 respectively, by 5-Endo-Trig cyclisation of the 3-alkenol system.

A ring contraction strategy toward a diastereoselective total synthesis of (+)-bakkenolide A.

A diastereoselective route to (+)-bakkenolide A is presented from the readily available optically active Wieland-Miescher ketone. This novel synthesis of this sesquiterpene lactone features the following as key stereoselective transformations: (i) the ring contraction reaction of a octalone mediated by thallium(III) nitrate (TTN); (ii) a hydrogenation to create the cis-fused junction; and (iii) the formation of the C7 quaternary center through an enolate intermediate. Furthermore, during this work, the absolute configuration of a trinorsesquiterpene isolated from Senecio humillimus was assigned.

A simple and efficient protocol for epoxidation of olefins using dimethyldioxirane

Abstract The reaction of a series of monoterpenic olefins and Δ4-octalins with dimethyldioxirane led to the corresponding epoxides in excellent yields. Remarkable diastereoselectivity was observed for the Δ4-octalins. The procedure consists simply in stirring the substrate, NaHCO3 and acetone, at 0°C, with dropwise addition of an aqueous solution of oxone.

Thallium trinitrate mediated ring contraction of monocyclic ketones: Stereochemical aspects

Abstract The reaction of 3- and 4-alkylcyclohexanones with thallium trinitrate (TTN) leads to the alkylcyclopentanecarboxylic acids in good yields and with high degree of stereoselectivity. The ring contraction of 2-methylcyclohexanone gives poor yields and 2,6-dimethylcyclohexanone does not undergo contraction. The observed diastereoselectivities of the reactions agree with the mechanism proposed by McKillop et al.

Cyclofunctionalization of unsaturated alcohols with aryltellurium trihalides

Abstract The reaction of unsaturated alcohols with aryltellurium trihalides leads to cyclic ethers bearing an aryldihalotelluro group in the β position, in high yields. Reduction of the tellurium-halogen bond with thiourea dioxide gives the corresponding tellurides in excellent yields.

Thallium trinitrate-mediated ring contraction of 1,2-dihydronaphthalenes: an approach to the synthesis of indans

Abstract Oxidation of 1,2-dihydronaphthalenes with thallium trinitrate was studied. 1,2-dihydronaphthalene, 1-methyl-1,2-dihydronaphthalene, 6- and 8-methoxy-1,2-dihydronaphthalenes gave rise to the respective ring contraction products in good yields, whereas the rearrangement was not observed using 4-methyl-1,2-dihydronaphthalene and 1-n-butyl-4-methyl-1,2-dihydronaphthalene as substrates.