Arene)Cr(CO) 3 ] complexes have found widespread application in organic synthesis as a result of the activating and stereodirecting influence of the p Lewis acid fragment Cr(CO) 3 . The applications include nucleophilic addition to the aromatic ring, to carbonyl and imine functions in side chains, and to configurationally stable benzylic carbocations. Arene lithiation reactions and reactions via benzylic anions also are much more facile in the complex than in the free arene. Diastereoselective and enantioselective variants have been developed for many transformations and they have found application in asymmetric organic synthesis and in the synthesis of chiral ligands for asymmetric catalysis. [1] [(benzene)Mo(CO) 3 ] is readily accessible from Mo(CO) 6 [2] but, surprisingly, analogous reactions to the ones listed above for the Cr(CO) 3 complex have not been reported. Intrigued by this situation, we started a research project on [(arene)Mo-(CO) 3 ] complexes and here report the first results.Thermochemical studies show the arene±Mo bond (68 kcal mol À1 in [(h 6 -C 6 H 6 )Mo(CO) 3 ] (1)) to be stronger than the arene±Cr bond (53 kcal mol À1 in [(h 6 -C 6 H 6 )Cr(CO) 3 ]) (2)). [3] MÀH bonds are also stronger with the second-row transition metal, as shown by the values of 62 kcal mol À1 and 54 kcal mol À1 in [CpMo(CO) 3 (H)] and [CpCr(CO) 3 (H)], respectively. [4] Kinetically, however, the situation is reversed. The metal±arene bond in 1 is far more labile than that in 2. This lability and the resulting difficulty in handling the Mo compounds have retarded their use in synthesis. We anticipated that there would be different selectivities in the reactions of the Cr and Mo complexes and that the higher bond strength of the MoÀC and MoÀH bonds would make possible the isolation of intermediates that have eluded characterization in the Cr-mediated reaction sequence. Both of these hypotheses have now been fulfilled.Addition of 2-lithio-1,3-dithiane [5] (2 a; Scheme 1) to a cold (À78 8C) solution of the benzene±Mo complex 1 in THF*** afforded a yellow precipitate 3 a, which dissolved when the reaction mixture was warmed to À20 8C. The 1 H NMR spectrum of 3 a was consistent with that expected for the anionic cyclohexadienyl complex. Treatment of the THF solution of 3 a with allyl bromide (4 a) produced the [(h 3allyl)(h 5 -cyclohexadienyl)Mo(CO) 2 ] complex (5 a) which was isolated as a yellow solid. In solution, 5 a is present as a mixture of the two rapidly interconverting exo±endo allyl isomers. Analogous reactions with [(h 6benzene)Cr(CO) 3 ] have been shown previously to give directly the decomplexed cyclohexadiene 6. [6] In the Cr-mediated reaction, metal allylation, followed by CO insertion, reductive elimination, and decomplexation occurred readily and intermediates could not be detected. In marked contrast to the above, the Mo±allyl complex 5 a is stable at room temperature. Its intermediacy on the pathway to a trans-disubstituted cyclohexadiene was shown by placing a solution of the complex 5 a under 4 atm of CO ...

For the synthesis of methyl jasmonate (1), via the strategic intermediates 3, 4, and 6a, we constructed a synthetic network via the diverse intermediates 7–10, 13, 14, 17, and 18. This allowed us to compare the efficiency of more than 20 novel routes. The most productive pathway with a total yield of 38% is represented by the sequence→5a→5m→13b→13a→6a→4 and proceeds via sequential bromination, basic elimination, decarbomethoxylation, isomerization, and finally Lindlar hydrogenation. The shortest selective way, 2a→[(E,E)‐12b]→3→4, is a two‐pot sequence using a modification of Naef's method, based on an aldol condensation between inexpensive cyclopentanone (2a) and crotonaldehyde, with in situ CoreyChaykovsky cyclopropanation under phase transfer conditions. The key intermediate 3 was then simply pyrolyzed to afford 4 in 27% total yield. The alternative isomerization method via the six‐step deviation→5a→5c→8c→13a→6a→4 was longer, although more efficient, with a total yield of 32%. Alternatively, a yield of 34% was obtained via the five‐step sequence→5a→5c→2h→2i→4. Another favored six‐step pathway,→5a→5c→2h→17a→14a→4 afforded the target compound in 35% total yield.

Treatment of cyclohexadecanone (1g; with I2 (2.2 mol‐euqiv.) and KOH in MeOH) furnished the unsaturated (Z)‐ester 2g in 83% yield, via a stereospecific Favorskii rearrangement (Scheme 1). Further treatment with 3‐chloroperbenzoic acid (m‐CPBA) afforded the unreported epoxy ester 3g (88% yield), which was cleaved in 33% yield to Exaltone® (=cyclopentadecanone; 1f) with NaOH in MeOH/H2O and then HCl at 65°. This methodology was similarly extended to higher (C17) and lower (C15 to C11) cyclic ketone analogues, as well as regioselectively to (−)‐(R)‐muscone (5c) and homomuscone (5f) (Scheme 2). Olfactive properties of the corresponding macrocyclic 1‐oxaspiro[2,n]alkanes and ‐alkenes 4 and 8, resulting from a CoreyChaykovsky oxiranylation, are also presented.

Three new (?2-acrylate)(?6-arene)dicarbonylchromium complexes are reported. They were obtained either by CO/acrylate exchange in [Cr(?6-benzene)(CO)3] (1) via the photolytically generated ?2-cyclooctene intermediate or by arene exchange in [Cr(?2-methyl acrylate)(?6-benzene)(CO)2] (3) (Scheme 1). On crystallization, [Cr(?2-methyl acrylate)(?6-o-xylene)(CO)2] (5) underwent partial resolution. The degree of this resolution was analyzed via X-ray crystal-structure determination (Fig. 1) and was correlated to the CD spectra in solution (Fig. 6), thus allowing the assignment of the absolute configuration. The reaction of [Cr(?2-acrylate)(?6-benzene)(CO)2] complexes with cyclopentad-1,3-diene or 1H-indene afforded new (?6-cyclopenta-2,4-dien-1-yl)- or (?6-1H-inden-1-yl)(?3-oxaallyl)chromium complexes (Scheme 2). A mechanism is proposed that involves arene-ligand substitution by the diene ligand, initiated by haptotropic rearrangement of the acrylate from a ?2- to a ?4-coordination mode, followed by hydride migration from the diene to the acrylate (Scheme 3). An X-ray crystal-structure determination of [Cr(CO)2(?5-1H-inden-1-yl){?3-CH(CH2CF3)C(O)OEt}] (8) reveals a metal enolate that is best described as ?3-oxaallyl species (Fig. 2). A shorter, more-efficient route to the [Cr(?5-1H-inden-1-yl)(?3-oxaallyl)] complexes was devised via the reaction of [Cr(CO)2(?2-cyclooctene)(?6-1H-indene)] with methyl acrylate (Scheme 4)