Both enantiomers of acetoxytubipofuran were synthesized using enantioselective and diastereoselective dearomatization sequences starting from the benzaldehyde chromium tricarbonyl complex. Following aldol condensation, a sequence involving Pd-catalyzed allylic substitution was used in the synthesis of the (-)-enantiomer, whereas the (+)-enantiomer was reached via an Eschenmoser-Claisen rearrangement. Chiroptical data show that a revision of the previously assigned absolute configuration of the natural product is required.

An efficient protecting group controlled regioselective chromium(0)-mediated three-component higher order cycloaddition of tethered diynes with cyclic trienes that generates five rings and six stereogenic centers in one step is described. Following a sequence of reactions featuring a chemoselective Baeyer-Villiger rearrangement and a regioselective cyclopropane hydrogenolysis, the total synthesis of 9-epi-pentalenic acid was achieved.

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A new strategy for the construction of the isotwistane skeleton is reported from easily available cyclohexadienes, which involves a one-pot cationic skeletal rearrangement and ene cyclisation of a bicyclo[2.2.2]octenone derivative and a cationic rearrangement of a tricyclo[5.3.0.0 4,8 ]decane to a [4.3.1.0 3,7 ]decane skeleton as the key steps in the synthesis of 2-pupukeanone.

An efficient dearomatization process of [Cr(arene)(CO) 3 ] complexes initiated by a nucleophilic acetaldehyde equivalent is detailed. It generates in a one-pot reaction three CÀC bonds and two stereogenic centers. This process allowed a rapid assembly of a cis-decalin ring system incorporating a homoannular diene unit in just two steps starting from aromatic precursors (Scheme 2). The method was applied to the total synthesis of the eudesmane-type marine furanosesquiterpene (AE)-15-acetoxytubipofuran (2). Two routes were successfully used to synthesize the g-lactone precursor of the furan ring. The key step in the first approach was a Pd-catalyzed allylic substitution (Scheme 3), while in the second approach, an Eschenmoser ± Claisen rearrangement was highly successful (Scheme 4). The Pd-catalyzed allylic substitution could be directed to give either the (normal) product with overall retention as major diastereoisomer or the unusual product with inversion of configuration (see Table). For the synthesis of the (À)-enantiomer (R,R)-2 of 15-acetoxytubipofuran, an enantioselective dearomatization in the presence of a chiral diether ligand was implemented (Scheme 7), while the ()-enantiomer (S,S)-2 was obtained via a diastereoselective dearomatization of an arene-bound chiral imine auxiliary (Scheme 8). Chiroptical data suggest that a revision of the previously assigned absolute configuration of the natural product is required.Introduction. ± Tricarbonylchromium-mediated dearomatization provides an efficient access to polysubstituted cyclohexadienes [1]. Up to three C-substituents can be added across an arene double bond in a one-pot procedure in a regio-and stereoselective manner by a sequential nucleophilic/electrophilic addition or by a nucleophilic addition followed by an acylation/alkylation sequence [2]. This dearomatization method has seen considerable development, with recent efforts mainly directed towards asymmetric variants of this reaction to give enantiomerically enriched products. Four different asymmetric methods have been developed: asymmetric induction with complexes of arenes bearing a chiral auxiliary as substituent [3], use of arene complexes possessing planar chirality [4], use of prochiral complexes with chiral nucleophiles [5], and use of complexes containing a chiral ligand at the chromium atom [6]. Benchmark enantio-and diastereoselectivities have been obtained in dearomatizations with these methods. In all but the last method, asymmetric induction takes place during the nucleophilic addition step. The third method offers an enantioselective variant in that chirality can be centered on an external ligand rather than on the nucleophile itself, and first results of the use of substoichiometric quantities of chiral information have been realized [7].In all of the dearomatization processes mentioned above, the products possess a homoannular cyclohexadiene moiety. This subunit embedded in a cis-decalin ring