Abstract:The tricarbonylchromium complex 3 of I ,2-dioxobenzocyclobutene (1) is easily prepared by hydrolysis of diacetal 4. Complex 3 stereoselectively undergoes both single and double nucleophilic addition reactions at the keto groups. As a consequence, addition of excess alkenyllithium to 3 gives rise to a dianionic oxyCope rearrangement yielding benzocyclooctenedione complexes with good diastereoselectivity. Trapping of the bis(eno1ate) intermediate with chlorotrimethylsilane gives bis(eno1ether) 23.Subsequent addition of two different dianionic oxy-Cope rearrangement. This alkenyllithium derivatives yields the results in the formation of benzoanellated asymmetrically substituted rearrange-bicyclo[3.3.0]octane derivatives and, in ment product 15. To some extent, depen-the case of I-cyclopentenyllithium as the dent on the method of hydrolysis, an in-alkenylmetal, in the tetraquinane system tramolecular aldol addition follows the 19. The trans-anellation of one of the cyclopentane rings in trans-20 has been verified by an X-ray structural analysis. The highly substituted rearrangement product 21/22 is formed only in small yield; in solution the bis(eno1) tautomeric form 22 is favored over diketone 21.

The chromium-benzyne ion Cr+-C H4 was generated in the gas phase by electron-impacbinduced loss of 5 CO from (~6-1,2-dioxocyclobuta~nzene)tricarbonylchromium(O). The gas-phase reactions of the Cr+-C& ions with methanol, ammonia, several alkanes, alkadienes, and aromatic species were studied by Fourier transform ion cyclotron resonance spectrometry (FT-ICR) using an external ion source. The results show that the bimolecular reactivity of the Cr+-C6H4 cations is determined by the C6H4 ligand, exhibiting the high reactivity of benzyne. No reactions due to a primary reaction at Cr+ are discovered. In moet of the reactions, the main product observed for the bimolecular reaction is Cr+ released from the complex by the great exothermicity of the d o n at the C$i, ligand. However, in the a s e of lees exothermic reactions and if the excess energy is removed from the reaction complex by "evaporati@ a neutral leaving group, Cr+ complexes are observed whose ligands arise from addition reactions of the reactants to C$4. This is the case for cycloadditions of benzene-d8 and naphthalene-d8 to Cr+-C6H4, where the adducts shll containing Cr+ as well as ions formed by loas of acetylene-d2 from the adducts are observed. Thus, in the family of transition-metal-cation-benzyne complexes, the cation is extraordinary in exhibiting reactivity exclusively at the benzyne ligand. IntroductionThe study of the gas-phase reactions of bare transition-metal cations with organic substrates during the last few years has given a wealth.of information about organometallic chemistry.' A typical gas-phase reaction of a transition-metal ion with a hydrocarbon is the oxidative insertion into C-H and C-C bonds. Besides the investigation of the reactivity of bare metal ions, a study of the modification of the reactivity of the central metal ions of mrdinatively unsaturated metal complexes by the ligands is a major field of research in metal-organic chemistry.2 Usually the complexation of ligands alters the reactivity

Nature 1991,353, 642-644. Analytisch reine Proben erhllt man durch einfache Filtration, anschlie-Bendes Waschen mit wasserfreiem EtOH und MeCN und Trocknen im Vakuum bei 100°C fur 2-6 h. Korrekte C,H,Ba,Si-Analyse fur 1 '3.25 HOCH,CH,OH. Kristalldaten fur 1 . 3.25 HOCH,CH,OH: triklin P i , a =10.151(8), b = 13.865(5), c = 15.709(6) A, C( = 102.90(3), / l = 91.04(3), y = 109.75(3)", V = 2018(1)A3,Z= 4,eb,, =1.70gcm~',p(MoK.) = 2.08mm-',F(000) = 1080, farbloses rechteckiges Pllttchen, 0.2 x 0.5 x 0.44 mm3, 13038 Reflexe gemessen mit 5" < 28 < 50", 9298 unabhdngige Reflexe, R,,, = 0.0312; 8999 Reflexe mit Fo 2 6a(F) verfeinert. Die Daten wurden auf einem rnit LT-2-Tieftemperatureinrichtung ausgestatteten Siemens-R3/v-Diffraktometer bei 175 K gesammelt, mit Absorptions-(4-Scans) und Sekundare-Extinktions-Korrektur. Die Struktur wurde mit Direkten Methoden gelost, mit Siemens-SHELXTL-PLUS-Programm verfeinert. Alle Nicht-H-Atome wurden anisotrop verfeinert, die H-Atome wurden mit Differenz-Fourier-Synthese lokalisiert und isotrop verfeinert. Das 0-Atom eines Kristallsolvens-Glycolmolekuls ist auf zwei Lagen fehlgeordnet mit verfeinerten Besetzungszahlen von 0.700(1) und 0.300(1). Das entsprechende H-Atom wurde nicht eingesetzt. 745 Parameter mit [w-' = a2(F) + 0.000382(F,)2] verfeinert, R = 0.0282, R, = 0.0374, Restelektronendichte maximal + 0.80 e A-3, minimal -0.82 e k 3 .Weitere Einzelheiten zur Kristallstrukturuntersuchung konnen beim Direktor des Cam-

THF-mediated arene exchange in [Mo(benzene)(CO)3] (1) at ambient temperature affords Mo(CO)3 complexes of substituted arenes in good yields (13 examples)

The syntheses of the tricarbonylchromium complexes 2 and 3 of 1‐oxobenzocyclobutene and 1‐hydroxybenzocyclobutene are described. Alcoholate 6 of 3 undergoes a ring opening to the corresponding ortho‐quinodimethane intermediate between −30 and −20°C, which is trapped by dienophiles with high diastereoselectivity. While with most dienophiles products with a 1,2‐cis configuration (7, 8, 10) are formed, vinyl sulfones react in an exo‐selective cycloaddition with formation of 1,2‐trans‐configurated cycloadducts (12, 13). The configuration of the cycloadduct with phenyl vinyl sulfone is confirmed by an X‐ray crystal structure analysis. As one of the important aspects of the chemistry of benzocyclobutene complexes is the chirality of compounds like 2 and 3, the enantiomeric resolution has been achieved via the semioxamazones of ketone 2.