Palladium-catalyzed cross-coupling reaction of 1,1-diboryl-1-alkenes with aryl and alkenyl iodides was found to proceed stereoselectively, giving rise to the corresponding mono-coupled product as a single diastereomer with E-configuration. Second coupling of the initial product with another aryl iodide affords diverse triarylalkenes in their stereochemically pure form. This highly stereoselective approach for triarylalkenes allows one to synthesize both diastereomers in one pot from 1,1-diboryl-1-alkenes.

Keywords: Cyclopropane / Palladium / Transition metal / Cascade reactions / ElectrocyclizationAcyclic 2-bromo-1,6-enynes 5-R, 9-R and 11-R with bulky substituents at the acetylenic terminus were co-cyclized with the highly strained bicyclopropylidene (12) under palladium catalysis at 80°C to give the cross-conjugated tetraenes 13-R, 18-R and 19-R in moderate-to-good yields (34−71%). Only the co-cyclization of 5-Ph gave rise to an additional product, which was identified as the 11-membered ring 20. At elevated temperatures (120−140°C) the initially formed tetraenes underwent 6π-electrocyclization to give spiro [cyclopropane-1,4Ј-bicylo[4.3.0]-1(6),2-dienes] 21-R, 22-R and 23-R. This novel class of spirocyclopropanated oligocycles is also accessible by a one-pot protocol. The highest yields for both

Cyclopropylidene lithium carbenoids reacted with bis(pinacolato)diboron in THF/Et2O at −110 °C to give various 1,1-diborylated cyclopropanes in good yields. Treatment of the diborylated cyclopropanes with 3-chloro-1-lithio-3-methyl-1-butyne produced the corresponding diborylated allenylcyclopropanes, which underwent ring-expansion in the presence of a Rh catalyst to give 1,2-diborylated methylenecyclopentenes conveniently.

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Enediynes with methylenecyclopropane moieties attached either through the three-membered ring or the double bond smoothly underwent cobalt-mediated [2+2+2] cocyclizations to give cyclopropane-fused and spirocyclopropanated cobaltcomplexed tricyclo[7.3.0.0 2,6 ]dodeca-1,6-dienes (1,2,3,3a,4, 6,7,8-octahydro-as-indacenes) under relatively mild conditions in yields ranging from 31 to 94 % (6 examples). Electron-withdrawing substituents at the acetylenic terminus of

Owing to the drastic advances in information technology, the development of fast, high-density 3D optical data storage is a key issue.[1] Consequently, much attention has been paid to multilayered recording to realize 3D data storage.[2] Meanwhile, holographic recording, by which information is stored as an optical interference pattern produced by two intersecting coherent object and reference beams, serves as a valuable method for optical data storage.[3] Therefore, holographic recording into a multilayered medium constitutes a highly promising approach for the realization of 3D optical memory with excellent performance. However, conventional holographic recording systems cannot be applied to this approach because the information recorded into a layer is erased when a read/write process is effected on other layers. To overcome the problem of such destructive processes, two-photon holographic recording appears to be an attractive method. This technique involves excitation of a p-conjugated organic molecule from a ground state (S 0 ) to a higher triplet state (T n ) via S 0 -S 1 absorption by a gate laser, subsequent intersystem crossing (S 1 to T 1 ), and finally T 1 -T n absorption by a holographic light consisting of object and reference beams (Scheme 1a).[4] The higher triplet state induces a photochemical reaction in the recording medium, resulting in a change of refractive index; that is, resulting in a data-writing process. In this system, only a layer irradiated by the gate light is photoreactive towards the holographic light, and any layers not subjected to gate irradiation remain intact during the storage and retrieval of data by the holographic light. Although a-diketones such as biacetyl and benzil dissolved in an a-cyanoacrylate polymer have been demonstrated to achieve such twophoton holographic recording, the diffraction efficiencies were not sufficient for realizing multilayered recording, probably because of the low molecular extinction coefficients for the S 0 -S 1 and T 1 -T n transitions. [5] Hence, the use of p-conjugated molecules that exhibit large molecular extinction coefficients at the transitions is ideal for high-performance, twophoton holographic recording. Oligothiophenes are attractive materials to fulfill such criteria, [6] but the T n states themselves cannot induce any chemical reactions at the recording medium. Therefore, we considered the simultaneous use of an acceptor that can receive energy from the T n state of the oligothiophenes and induce chemical reactions to result in data writing (Scheme 1b). Reported herein is a novel strategy for efficient two-photon holographic recording that involves twophoton absorption of an a-quinquethiophene and subsequent energy transfer to an aryl azide.In the beginning, we focused our attention on a-quinquethiophene (1a: R = H) as a two-photon absorber because its UV and T-T absorption maxima (417 nm and 630 nm, re-COMMUNICATION 1826

The boryl group cis to the C(3)=C(4) group in 2,4-aryl-1,1-bis(pinacolatoboryl)-1,3-butadienes undergoes Pd-catalyzed cross-coupling reaction with aryl iodides stereoselectively at room temperature, giving rise to the corresponding boronates as a single diastereomer. Subsequent coupling of the boronates with alkenyl iodides allows us to synthesize 1,3,4,6-tetraarylated 1,3,5-hexatrienes stereoselectively.

2-Bromotetradec-1-ene-7,13-diynes 1, 5, 12 with different substituents at the acetylenic terminus under palladium catalysis have been found to either yield an angularly bisannelated benzene derivative 3 (79%), or fulvene derivatives of type 5 (52-74%) as well as monoannelated fulvenes 13b-e (32-48%). The mechanisms for all three reaction modes most probably involve intramolecular 5-exo-trig carbopalladations of an intermediate 1,3,5-hexatrienyl-6-palladium bromide intermediate. Transition-metal-catalyzed C-C-bond forming reactions have been widely explored in the past 15 years. Among them, palladium-catalyzed cross-couplings have attracted considerable attention in both academic and industrial research laboratories.1 Towards the construction of complex organic molecules from relatively simple open chain precursors, the Heck reaction is particularly attractive, as it is compatible with a variety of functional groups and can be incorporated more than once in multistep sequential processes 2 following a number of distinctly different reaction pathways.1,3 Thus, single operation tricyclizations of 2-bromoalk-1-enediynes have been used to prepare carbocyclic as well as heterocyclic angularly bisannelated benzene derivatives in moderate to good yields. 4 All previously reported examples, however, contained either two five-or one five-and one six-membered ring attached to the aromatic central ring. In order to test the accessibility of the octahydrophenanthrene skeleton by this route, we have prepared several 2-bromotetradec-1-ene-7,13-diynes and subjected them to typical Heck cross-coupling conditions. 5Upon treatment of dimethyl 2-bromo-14-(tert-butyldimethylsilyl)-tetradec-1-ene-7,13-diyne-4,4-dicarboxylate (1) with palladium acetate in the presence of triphenylphosphine and potassium carbonate in acetonitrile at 60°C for 20 h, it was smoothly converted into dimethyl (9-tert-butyldimethylsilyl)-1,2,3,4,5,6,7,8-octahydrophenanthrene-2,2-dicarboxylate (3).6 This transformation appears to have proceeded via a 6-endo-trig cyclization or a 6p-electrocyclization of the alkenylpalladium intermediate 2, (Scheme 1), followed by a,b-dehydropalladation. In contrast, dimethyl 2-bromotetradec-1-ene-7,13-diyne-4,4-dicarboxylate (4a) which was obtained from 1 by hydrodesilylation at the acetylenic terminus, under identical conditions did not yield the unsilylated octahydrophenanthrene, but the bisannelated fulvene derivative 5a within 1 h in 74% yield (Scheme 2).7 The 9-methoxy-substituted analog 4b and the heteroanalogous bromoenediyne 4c, under slightly modified conditions, reacted in the same way to give the fulvenes 5b in 65% yield within 45 min, and 5c in 52% yield within 1.5 h, respectively. The structure of the fulvene 5b was rigorously proved by an X-ray crystal structure analysis of the Diels-Alder adduct that was readily formed upon treatment of 5b with dimethyl acetylenedicarboxylate (Figure). 8 The formation of fulvenes 5 may be rationalized in terms of a 5-exo-trig-carbopalladation instead of the 6-endotr...