Geminal Difunctionalization of Alkenylidene-Type Carbenoids by Using Interelement Compounds

Access to 1,1‐Diborylalkenes and Concomitant Stereoselective Reactivity

“…Double cross‐coupling of 1,1‐diborylalkenes has also been developed, with the goal of joint conversion of both C–B bonds into C–C bonds. Hence, Shimizu, Hiyama and co‐workers developed a convenient Pd(PPh 3 ) 4 ‐catalyzed double arylation of 1,1‐diborylmethylenecyclohexane with iodobenzene at 70 °C (Scheme a). Similarly, Jin and co‐workers demonstrated the synthetic usefulness of 1,1‐diborylalkenes by means of double annulative Suzuki–Miyaura coupling with 2,2′‐dibromo‐1,1′‐biphenyl reagent in the presence of Pd(PPh 3 ) 4 catalyst.…”

“…Hiyama and Shimizu discovered in 2001 that alkylidene‐type lithium carbenoids can react with bis(pinacolato)diboron (B 2 pin 2 ), allowing the conversion of 1,1‐dihaloalkenes or 1‐haloalkenes into 1,1‐diborylalkenes (Scheme ). BuLi or LiTMP are usually employed to form alkylidene‐type lithium carbenoids, and this can even take place in a stereoselective manner, particularly when the substrate contains a control element, such as an alkoxy group (Scheme ), that assists stereoselective bromine‐to‐lithium exchange.…”

Synthesis of Triborylalkenes from Terminal Alkynes by Iridium‐Catalyzed Tandem CH Borylation and Diboration

“…1,1‐Diborylalkenes can be made from either 1,1‐dichloro‐ or 1,1‐dibromoalkenes through lithium–halide exchange and subsequent reaction with bis(pinacolato)diboron (B 2 pin 2 ; Figure 1 a). 7, 8 Alternatively, they can be accessed by hydroboration of alkynylboronates,9 or by dehydrogenative borylation of alkenes with diboron reagents 10. Metal‐catalyzed addition of diboron reagents to terminal or internal alkynes leads to 1,2‐ cis ‐diborylalkenes (Figure 1 b).…”

Metal‐Catalyzed Cross‐Coupling Reactions of Organoboron Compounds with Organic Halides

“…The utility of the benzannulation-crosscoupling sequence has been demonstrated in the synthesis of a dimeric carbazole, bis-N-dimethylbismurrayaquinone A. The reaction between lithium carbenoids and diboron (13) or silylboron (14) [87] is particularly attractive for preparing a new class of boron compounds such as 1,1-bisborylalkenes and 1-silyl-1-borylalkenes (64) [87][88][89]. The addition of 14 to a solution of alkenylidene carbenoid at -110 hC forms an ate-complex (63), which is then followed by intramolecular S N 2 substitution with complete inversion of the configuration at the a-carbon.…”

“…The reactions of allyl acetate or phenoxide [108], propargyl carbonates [109], 1,3-butadiene monoxide [110], phenyl trifluoroacetate [111], and carboxylic acid anhydrides [112] proceed in the absence of bases, because oxidative addition yields RO-Pd species (87)(88)(89)(90)(91) which can transmetallate with organoboron compounds. Among these intermediates, the reaction of phenylboronic acid with 91 has been shown to occur at room temperature under neutral conditions [111].…”