Recently, numerous multiple bond species containing heavier group 14 elements have been isolated and characterized. 1 In particular, considerable interest has been focused on the nature of alkene analogues of silicon 2 because of their unusual structures and bonding since the isolation of a stable tetramesityldisilene by West and co-workers. 3 In many cases, the π bond of the disilenes has displayed an increased reactivity toward many reagents, compared with that of alkenes and alkynes, because of the relatively small HOMO-LUMO gap and its biradical character. 4 For example, the π bond of disilenes is known to undergo smooth [2 + 2] cycloadditions toward alkenes and alkynes to give the disilacyclobutane and disilacyclobutene derivatives, respectively. 1,2 On the other hand, much less is known about the π bond nature of disilynes with a silicon-silicon triple bond, which has two distinct π bonds (π in and π out ), 5,6 although a few papers have described the reactivity of alkyne analogues. 7 Now, a comparison of the chemical behavior of heavier group 14 element alkyne analogues with that of alkynes is of special interest. To understand the nature of the π bond of a silicon-silicon triple bond, we have examined the reaction of disilyne 1 5a with alkenes and alkynes. In this paper, we present the results of the stereospecific cycloadditions of 1 to 2-butenes, 8 together with those of the cycloaddition of 1 to phenylacetylene to give an isolable 1,2-disilabenzene derivative. Furthermore, we report theoretical studies on the mechanism of the reactions, showing that these reactions involve in the initial step [1 + 2] cycloaddition (the interaction between the LUMO (π in *) of 1 and the HOMO of 2-butenes or acetylene), instead of a direct [2 + 2] cycloaddition.When a hexane solution of disilyne 1 was treated with an excess of cis-2-butene at room temperature, cis-3,4-dimethyl-1,2-disilacyclobutene 2a was obtained as the sole product in 89% yield (Scheme 1). 9 This reaction proceeded cleanly and was complete within 30 min. On the other hand, the reaction of 1 with trans-2-butene under the same conditions produced trans-3,4-dimethyl-1,2-disilacyclobutene 2b as yellow crystals in 85% yield. 9 In contrast to the reaction with cis-2-butene, it took 1 day to complete this reaction. Most importantly, both reactions proceeded stereospecifically, as was determined by NMR spectra and X-ray analysis (for 2b). 9 Although an excess of 2-butenes was used in both reactions, the subsequent cycloaddition reaction was not observed.To gain a mechanistic insight, we have performed theoretical calculations of the reaction of disilyne 1 with 2-butenes. Figure 1 shows the energy profile along the reaction path calculated at the B3LYP/[Si, 6-311+G(2df); C and H, 6-31G(d)]//B3LYP/3-21G* level. 10 The interaction between the in-plane LUMO (π in *) of 1 and the HOMO of 2-butene, resulting in [1 + 2] cycloaddition, is the first step in both reactions to produce the silacyclopropylsilylene intermediate (Int1). 11 The alternative interaction between...

Trans-metalation process in the palladium-catalyzed borylation of iodobenzene with diboron was theoretically investigated with the DFT method. Palladium(II) hydroxo phenyl complex, Pd(OH)(Ph)(PH(3))(2), and the fluoro analogue easily undergo the trans-metalation with diboron, B(2)(eg)(2) (eg = -OCH(2)CH(2)O-), to afford Pd(Ph)(Beg)(PH(3))(HO-Beg) and Pd(Ph)(Beg)(PH(3))(F-Beg), respectively, where B(2)(eg)(2) is adopted as a model of bis(pinacolato)diboron used experimentally. The electron re-distribution in the trans-metalation clearly indicates that the B-B bond scission occurs in a heterolytic manner. In the chloro analogue, PdCl(Ph)(PH(3))(2), however, the trans-metalation occurs in a homolytic manner with much difficulty, which is consistent with the experimental result. The significant differences between the chloro complex and the other hydroxo and fluoro complexes are easily interpreted in terms that hydroxo and fluoro ligands can form strongly bonding interaction with B(2)(eg)(2) but the chloro ligand cannot.

A concise two one-pot synthesis of WIN 64821, eurocristatine, 15,15'-bis-epi-eurocristatine, ditryptophenaline, ditryptoleucine A, WIN 64745, cristatumin C, asperdimin, naseseazine A, and naseseazine B is detailed, based on a unique bioinspired dimerization reaction of tryptophan derivatives in aqueous acidic solution and a one-pot procedure for the construction of diketopiperazine rings. Total yields of these alkaloid syntheses were from 10 up to 27 %. In addition, 1'-(2-phenylethylene)-ditryptophenaline was synthesized by using three one-pot operations. The studies detailed herein provided synthesized natural products for inhibitory activities of ubiquitin-specific protease 7 (USP7) and foam cell formation in macrophages. The newly listed biological evaluation for tryptophan-based dimeric diketopiperazine alkaloids discovered 15,15'-bis-epi-eurocristatine, 1'-(2-phenylethylene)-ditryptophenaline, and WIN 64745 as new drug candidates.