A Concise Diastereoselective Total Synthesis of α-Ambrinol.

(-)--α-Ambrinol is a natural product present in ambergris, a substance of marine origin that has been highly valued by perfumers. In this paper, we present a new approach to its total synthesis. The starting material is commercially available α-ionone and the key step is an intramolecular Barbier-type cyclization induced by CpTiCl, an organometallic compound prepared in situ by a CpTiCl reduction with Mn.

Enantioselective total synthesis of putative dihydrorosefuran, a monoterpene with an unique 2,5-dihydrofuran structure.

An original synthesis of the structure of dihydrorosefuran, a compound allegedly identified in and , has been developed. The key steps in the five-step 36% overall yield synthesis are a CpTiCl mediated Barbier-type allenylation of a linear aldehyde and the formation of a 2,5-dihydrofuran scaffold through a Ag(I)-mediated cyclization. Neither of the reported spectral data for dihydrorosefuran match those of the synthetic product, suggesting that the isolated compound from is in fact the natural product rosiridol, while the real structure of the product from remains unknown.

Marine Terpenic Endoperoxides.

Organic extracts of marine invertebrates, mainly sponges, from seas all over the world are well known for their high in vitro anticancer and antibiotic activities which make them promising sources of compounds with potential use as pharmaceutical leads. Most of the structures discovered so far have a peculiar structural feature in common: a 1,2-dioxane ring. This is a highly reactive heterocycle that can be considered as an endoperoxide function.

Stereoselective Barbier-Type Allylations and Propargylations Mediated by CpTiCl.

CpTiCl, prepared in situ by manganese reduction of CpTiCl, is an excellent new system for the Barbier-type allylation and propargylation of carbonyl compounds. It can be used in catalytic amounts when combined with EtN·HBr/TMSBr, which acts as a regenerating system. The high regio- and stereoselectivity shown by this system makes it useful for prenylation and crotylation processes in the synthesis of natural products.

Ti-catalyzed homolytic opening of ozonides: a sustainable C-C bond-forming reaction.

The unprecedented homolytic opening of ozonides promoted and catalyzed by titanocene(III) is reported. This novel reaction proceeds at room temperature under neutral, mild conditions compatible with many functional groups and provides carbon radicals suitable to form C-C bonds via both homocoupling and cross-coupling processes. The procedure has been advantageously exploited for the straightforward synthesis of the natural product brittonin A.

Synthesis of pterocarpans.

The total synthesis of natural pterocarpans and analogs is reviewed.

Reaction of benzoxasilocines with aromatic aldehydes: Synthesis of homopterocarpans.

Condensation of 2H-benzo[g][1,2]oxasilocines with aromatic aldehydes in the presence of boron trifluoride affords mixtures of cis/trans 2-phenyl-3-vinylchromans with moderate yields. These can be transformed into homopterocarpans, a synthetic group of substances homologous to the natural isoflavonoid pterocarpans.

Diastereoselective synthesis of 2-aryl-3-vinyl-2,3-dihydrobenzo[b]furans through a Sakurai reaction: a mechanistic proposal.

The condensation of 2,3-dihydrobenzoxasilepins with aromatic aldehydes in the presence of boron trifluoride to form 2,3-dihydrobenzofurans shows a level of diastereoselection which is a function of the electronic nature of the aldehyde and the polarity of the solvent. The study of the mechanism of the reaction demonstrated that it proceeds through a ring-opened allylfluorosilane, which is stable enough to be isolated and characterized.

Silver-catalyzed asymmetric synthesis of 2,3-dihydrobenzofurans: a new chiral synthesis of pterocarpans.

2,3-Dihydrobenzofurans can be diastereoselectively prepared by condensation of aromatic aldehydes with 2,3-dihydrobenzoxasilepines under the catalysis of Ag(I) complexes, and in the presence of a source of fluoride ion. The application of this strategy by using chiral catalysts leads to a new enantioselective total synthesis of natural cis-pterocarpans and their trans isomers. Through this method, the first enantioselective total synthesis of the antifungal agent (-)-pterocarpin was achieved.

A concise and diastereoselective total synthesis of cis and trans-pterocarpans.

A new strategy for the diastereoselective and convergent synthesis of pterocarpans which is able to control the relative stereochemistry of the molecule through allylation of aromatic aldehydes with cyclic allylsiloxanes is described.