An Opened Route to 1,3-Dimethylenecyclobutanes via Sequential Ruthenium-Catalyzed [2 + 2] Cycloaddition of Allenyl Boronate and Palladium Suzuki Coupling

Abstract

The regioselective head-to-head [2 + 2] cyclodimerization of allenyl boronate catalyzed by the ruthenium catalyst [Cp*RuCl(COD)] leads to a novel diboronated 1,3-dimethylenecyclobutane. Consecutive palladium-catalyzed C-C couplings open a route to novel disubstituted 1,3-dimethylenecyclobutane species. The X-ray crystalline structure of the phenyl-substituted 1,3-dimethylenecyclobutane is provided.

Exploiting [2+2] cycloaddition chemistry: achievements with allenes

“…92 In 2003, Akiyama and co-workers studied the enantioselective [2+2] cycloaddition reaction of 1-methoxyallenylsilanes 259 with an a-imino ester catalyzed by the system [Cu (MeCN) 4 ]BF 4 /(R)-Tol-BINAP, affording 3-methyleneazetidine-2-carboxylates 260 in good yields (60-90%) and with excellent enantiomeric excesses (58-97%). 93 Besides, the acid-catalyzed ring opening of the azetidines 260 has opened a new route to access homochiral acylsilanes 261 quantitatively (Scheme 86).…”

Transition metals in organic synthesis: Highlights for the year 2005

“…Ruthenium catalyzed a [2 + 2]cycloaddition of allenylboronates [1279]. Iron catalyzed asymmetric Staudinger reactions to form ␤-lactams [1280].…”

The Antiferromagnetic Spin Coupling in Non‐Kekulé Acenes—Impressive Polyradical Character Revealed by High‐Level Multireference Methods

“…Additional synthetic routes for the preparation of DMCBD have also been suggested, such as gasphase generation with oxygen anions, [20] syntheses that involve different derivatives of bicyclo[1.1.0] butanes, [21] and the most recent example of ruthenium-catalyzed cycloaddition of allenyl boronate and subsequent palladium Suzuki coupling. [22] Complete active space (CASSCF) and multireference (MR-CISD(Q) and MR-AQCC) calculations were performed for nonKekulØ analogues of acenes, dimethylenepolycyclobutadienes, with lengths of up to eight cyclobutadiene (CBD) units. Multireference calculations predict that the most stable energy state of the system is either triplet (if there is an odd number of CBD units) or singlet (if there is an even number of CBD units) due to antiferromagnetic spin coupling, which thus violates Hund's rule in larger molecules.…”