Synthesis of 3-hydroxy-1-alkenylboronates via phosphine stabilized borylzirconacyclopropenes

Abstract

Zirconacyclopropenylboronates can be stabilized to dimerization by complexation with tributylphosphine; the phosphine stabilized zirconacycle boronates react with aliphatic and aromatic ketones and aldehydes at C2 of the triple bond to give the previously unknown 3-hydroxyvinylboronates in 61-80% isolated yields.

Synthesis of diethyl 2-(aryl)vinylphosphonates by the Heck reaction catalysed by well-defined palladium complexes

“…Interestingly, under these conditions the reaction temperature can be lowered up to 90°C giving still high conversions (Table 1, entry 3), the optimised conditions being achieved at 110°C in DMF with K 2 CO 3 as base (Table 1, entry 2). Under these conditions weak influence of the palladium source was observed given that K 2 CO 3 or Et 3 N are used (Table 1, entries 2, 6,11,13,14,16). Unexpectedly, while commonly used in Heck coupling reaction, NMP as solvent led to low conversions at 110°C whatever the base used and we had to perform the reaction at 140°C to get significant yields (Table 1, entries 5 and 8).…”

“…Organometallic approaches include the syn-addition of organocuprates to 1-alkynylphosphonates [13,14], anti-hydrotelluration of 1-alkynylphosphonates [15], the formation of titanacycles from 1-alkynylphosphonates [16,17], the reaction of a-stannylated phosphonates with aldehydes to give E/Z mixtures [18], hydrozirconation of alkynes followed by phosphorylation [19,20], and olefin metathesis [21]. These methods are sometimes difficult to handle and often intolerant towards sensitive functional groups.…”

Carbometallation Reactions

“…Remarkably, compound 302 can be transformed to 300a, a structural isomer of the tetraalkylethene 300, in three simple chemical steps with exceptional isomeric purity of >99% (Scheme 10.100, inset). A transformation of alkynylboronates to functionalized trisubstituted alkenylboronates employing the Negishi reagent was reported earlier by Srebnik et al [83]. 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).…”

“…10.101 Synthesis of functionalized alkenylboronates via phospine-stabilized zirconacyclopropenes[83].…”

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

“…We reasoned that phosphine coordination should also be effective in stabilizing borylzirconacyclopropenes obtained by zirconation of 1-alkynylboronates with Negishi reagent (Cp 2 ZrCl 2 /2n-BuLi) [13]. Indeed, we have recently demonstrated this to be the case in the synthesis of 3-hydroxyvinylboronates which we could not prepare previously [14]. In this communication we report our results in the preparation of Bu 3 P stabilized borylzirconacyclopropenes and their reaction with terminal and internal alkynes to give primarily 2-boryl-1,3-dienes (Scheme 2).…”