José A. Bacigaluppo

Resolution and absolute configuration of a tricyclic lactone. A potentially useful precursor of highly functionalized terpenoids

Abstract The highly functionalized tricyclic lactone 1 was obtained in optically pure form by the sulfoximine-mediated resolution of the enone methyl acetal 3. The absolute configuration of (−)-3 and consequently of (+)-1, was determined by the transformation of (−)-3 into (−)-5, a known intermediate in the total synthesis of forskolin (2) and confirmed by application of the high field FT NMR Mosher method to alcohol 6.

An efficient and environmentally benign chemical synthesis of testolactone

A comparative study of two approaches for the chemical synthesis of the biologically interesting steroid testolactone is described. The first approach is efficient but classical, in the second one, hazardous chemicals were replaced by benign alternatives maintaining the same degree of efficiency.

THE MICHAEL-ALDOL CONDENSATION APPROACH TO THE CONSTRUCTION OF KEY INTERMEDIATES IN THE SYNTHESIS OF TERPENOID NATURAL PRODUCTS

Short routes for the preparation of highly oxygenated decalines, key intermediates for the synthesis of nimbolide m, by a sequence involving a Michael addition followed by an aldol condensation, are described. Many terpenoid products possessing a variety of structures were isolated from Azadirachta indica Juss. (Meliaceae), the Indias famed neem tree.1 Of this large group of natural products, azadirachtin (lJ has received increasing attention from a synthetic point of view due to its remarkable insecticidal properties.2 More recently, two structurally less complex tetranortriterpenoids, nimbolide (a and 28deoxonimbolide a), showing promising biological activity were also isolated from this interesting plant.3

Enantioselective synthesis of the white key intermediate for the synthesis of trisporic acids

Abstract The asymmetric construction of the alkylated cyclohexenone carboxylic acid moiety of trisporic acids A, B and C and the syntheses of related precursors are described. The syntheses feature a Michael addition in tandem with an aldol condensation as the central step.

CONVENIENT AND SHORT ROUTE TO A KEY INTERMEDIATE IN THE SYNTHESIS OF FORSKOLIN

Abstract The intermediate 2, previously used in several synthetic sequences toward forskolin (1), has been synthesized from enone 3. The key step in the sequence is the 1,3-oxidative rearrangement of the tertiary alcohol 5, which allowed the easy introduction of the keto group at C-6 of 2.

The Michael-Aldol Condensation Approach to the Construction of Key Intermediates in the Synthesis of Nimbolide and Nagilactone A

Abstract A short route for the preparation of highly oxygenated trans-decalines, key intermediates for the synthesis of nimbolide (2a) and nagilactone A (13), by a sequence involving a Michael addition followed by an aldol condensation, is described.

A practical and efficient synthesis of the ziegler key intermediate for the synthesis of forskolin

The Ziegler intermediate 2, previously used in three total syntheses of forskolin (1), has been synthesized efficiently from enone 3. The key transformation of this sequence is the early and stereoselecrive introduction of the C-6, C-7 oxygen functional groups present in the natural product.

Studies on a New Synthetic Route towards Cassiol

The synthesis of the acyclic intermediate 7 towards the preparation of cassiol (2) is described. The cyclization of 7 led to 5, a precursor of 2 and to the unexpected product 8.

Applications of Olefination Reactions to Cassiol Synthesis

Olefination reactions directed to the synthesis of cassiol from compounds 2-5 will be discussed.

Synthetic and structural studies of key intermediates toward forskolin and/or erigerol. Relative stereochemistry, conformational preferences and stereoselectivity control

An alternative stereoselective synthesis of compound 9c, an intermediate in the synthesis of the highly oxygenated diterpene erigerol 2, was accomplished through an organometallic addition to the α,β-unsaturated ketone 7, followed by osmylation and protection of the resultant diol. In spite of the fact that the addition of the Iithio derivative of N,S-dimethyl-S-phenylsulfoximide occurred exclusively from the β face of enone 7, this approach to the alcohol 8c, a key intermediate toward forskolin 1, is not suitable because of the low yield of the osmylation step. With the aid of one- and two-dimensional NMR techniques and a series of NOE experiments, the complete stereochemistry and conformational preferences of alcohols 8a, 8c, 9a and 9c were established. The lowest-energy conformations of alcohols 8a, 8c and 9c, based on molecular mechanics calculations, confirmed the results obtained by NMR spectroscopy.