Regio- and Diastereoselective Synthesis of Trisubstituted Alkenes Through Hydroalkylation of Alkynyl Boronamides.

Hydroalkylation of alkynes is a powerful method for alkene synthesis. However, regioselectivity has been difficult to achieve in transformations of internal alkynes hindering applications in the synthesis of trisubstituted alkenes. To overcome these limitations, we explored using boryl groups as versatile directing groups that can control the regioselectivity of the hydroalkylation and subsequently be replaced in a cross-coupling reaction. The result of our exploration is a nickel-catalyzed hydroalkylation of alkynyl boronamides that provides access to a wide range of trisubstituted alkenes with high regio- and diastereoselectivity. The reaction can be accomplished with a variety of coupling partners, including primary and secondary alkyl iodides, α-bromo esters, α-chloro phthalimides, and α-chloro boronic esters. Preliminary studies of the reaction mechanism provide evidence for the hydrometalation mechanism and the formation of alkyl radical intermediates.

Stereospecific and Regioselective Synthesis of E-Allylic Alcohols through Reductive Cross Coupling of Terminal Alkynes.

We have developed a convergent method for the synthesis of allylic alcohols that involves a reductive coupling of terminal alkynes with α-chloro boronic esters. The new method affords allylic alcohols with excellent regioselectivity (anti-Markovnikov) and an E/Z ratio greater than 200:1. The reaction can be performed in the presence of a wide range of functional groups and has a substrate scope that complements the stoichiometric alkenylation of α-chloro boronic esters performed using alkenyl lithium and Grignard reagents. The transformation is stereospecific and allows for the robust and highly selective synthesis of chiral allylic alcohols. Our studies support a mechanism that involves hydrocupration of the alkyne and cross-coupling of the alkenyl copper intermediate with α-chloro boronic esters. Experimental evidence excludes a radical mechanism of the cross-coupling step and is consistent with the formation of a boron-ate intermediate and a 1,2-metalate shift.

Base-Promoted Tandem Synthesis of 2-Azaaryl Tetrahydroquinolines.

A novel method to synthesize 2-azaaryl tetrahydroquinolines by the base-promoted tandem reaction of azaaryl methyl amines and styrene derivatives is reported (over 30 examples, yields up to 95%). Mechanistic probe experiments demonstrate that the deprotonation of the benzylic C-H bond and the addition to the styrene vinyl group proceeds via the SNAr mechanism.

Comparison of Fused-Ring Electron Acceptors with One- and Multidimensional Conformations.

Three fused-ring electron acceptors (FXIC-1, FXIC-2, and FXIC-3) were designed and synthesized. This FXIC series has similar electron-rich central units and the same electron-poor termini. Due to the different steric structures of fluorene, bifluorenylidene, and spirobifluorene, FXIC-1 is a one-dimensional (1D) crystal, while FXIC-2 and FXIC-3 are multidimensional (MD) amorphous materials. The conformations of the FXIC series have a slight impact on their absorption and energy levels. FXIC-1 has higher electron mobility than FXIC-2 and FXIC-3. When blending with different polymer donors (PTB7-Th, J71, and PM7), the FXIC-1-based organic solar cells have efficiencies higher than those of the FXIC-2/FXIC-3-based cells. Meanwhile, the ternary-blend cells based on PTB7-Th:F8IC with FXIC-1, FXIC-2, and FXIC-3 show similar efficiencies, which are all better than those of the binary-blend devices.

Fused Tris(thienothiophene)-Based Electron Acceptor with Strong Near-Infrared Absorption for High-Performance As-Cast Solar Cells.

A fused tris(thienothiophene) (3TT) building block is designed and synthesized with strong electron-donating and molecular packing properties, where three thienothiophene units are condensed with two cyclopentadienyl rings. Based on 3TT, a fused octacylic electron acceptor (FOIC) is designed and synthesized, using strong electron-withdrawing 2-(5/6-fluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)-malononitrile as end groups. FOIC exhibits absorption in 600-950 nm region peaked at 836 nm with extinction coefficient of up to 2 × 105 m-1 cm-1 , low bandgap of 1.32 eV, and high electron mobility of 1.2 × 10-3 cm2 V-1 s-1 . Compared with its counterpart ITIC3 based on indacenothienothiophene core, FOIC exhibits significantly upshifted highest occupied molecular orbital level, slightly downshifted lowest unoccupied molecular orbital level, significantly redshifted absorption, and higher mobility. The as-cast organic solar cells (OSCs) based on blends of PTB7-Th donor and FOIC acceptor without additional treatments exhibit power conversion efficiencies (PCEs) as high as 12.0%, which is much higher than that of PTB7-Th: ITIC3 (8.09%). The as-cast semitransparent OSCs based on the same blends show PCEs of up to 10.3% with an average visible transmittance of 37.4%.