Synthesis of 2-boryl-1,3-butadienes from tributylphosphine stabilized zirconacyclopropenes and alkynes

Recent Advances in Boron‐Substituted 1,3‐Dienes Chemistry: Synthesis and Application

“…Moreover, the use of the stabilized borylated zirconcyclopropenes from alkynylboronates in the presence of Cp 2 ZrCl 2 /2 n BuLi and Bu 3 P as a ligand leads to substituted alkynylboronates (Scheme ) . The reaction between various alkynes and zirconcyclopropenes gives 2‐boryl‐1,3‐butadienes 185 as main products (in 40–81 % isolated yield) accompanied by 1‐boryl‐1,3‐butadienes 186 (Scheme ) . The same authors showed that stabilized zirconacyclopropenes 183 also successfully reacted with aldehydes and ketones and generated oxazirconacyclopentenes, which in the presence of HCl/Et 2 O led to 3‐hydroxy‐1‐alkenylboronates .…”

“…Then internal alkyne is inserted into the B−Pd bond with high regioselectivity and (β‐borylalkenyl)chloropalladium(II) complex B is generated. A transmetallation involving organozirconium compound, generating the diorganopalladium complex C , is then followed by a reductive elimination of the boryl‐substituted product D (Scheme ) …”

Copper‐Catalyzed Borylation of α‐Alkoxy Allenes with Bis(pinacolato)diboron: Efficient Synthesis of 2‐Boryl 1,3‐Butadienes

“…In sharp contrast, the synthetic methods available to date for the synthesis of 2 ‐ boryl 1,3‐butadienes are not so efficient 8. For example, elaborate methods, including the enyne metathesis of alkynyl boranes8a–c (Scheme ), palladium‐catalyzed cross‐coupling reactions of ( Z )‐1‐halo 1‐alkenyl boranes8d or 1,1‐diboryl 1‐alkenes8e (Scheme ), reactions of alkynyl boranes with alkynes8f (Scheme ), and hydroboration followed by migration8g (Scheme ), have been reported; however, the variety of available 2‐boryl 1,3‐butadienes has remained quite limited. Thus, more efficient and general synthetic methods are highly desirable.…”

Carbometallation Reactions

“…The authors used tributylphosphine to stabilize the intermediate species that allowed the successful preparation of stable borylzirconacyclopropenes that were then treated with different aldehydes and ketones (Scheme 10.101). In a subsequent study, it has been shown that the phosphine-stabilized zirconacyclopropene species 304 were capable of the metallacycle expansion on reaction with mono-and disubstituted alkynes [84]. With this methodology, 1-boryl-1,3-butadienes were prepared in good chemical yields and with moderate to excellent stereoselectivity (Scheme 10.102).…”

“…With this methodology, 1-boryl-1,3-butadienes were prepared in good chemical yields and with moderate to excellent stereoselectivity (Scheme 10.102). Scheme 10.102 Synthesis of 1-boryl-1,3-butadienes from zirconacyclopropenes stabilized by a phosphine ligand [84].…”