Palladium(0) versus Nickel(0) Catalysis in Selective Functional‐Group‐Tolerant sp³–sp³ Carbon–Carbon Bond Formations

Abstract

We have uncovered Pd(0)-catalyzed intermolecular nonsymmetrical Suzuki-Miyaura-type sp(3)-sp(3) C-C bond formations between allyl carbonates and nontoxic allyl, allenyl, or propargyl boronates. This report represents the first use of these types of boronic esters in this particular context. The present transformations proceeded with high selectivity under remarkably mild conditions, and various functional groups including an aldehyde function proved to be compatible. In addition, several boronates were found to display very unusual reactivity patterns; the higher reactivity of boron as apposed to silicon was clearly demonstrated as well. Finally, the inherent problem of beta-hydride elimination associated with intermediary allyl-Pd species was addressed by employing a commercially available Ni(0) catalyst.

Enantioselective Synthesis and Cross‐Coupling of Tertiary Propargylic Boronic Esters Using Lithiation–Borylation of Propargylic Carbamates

“…We propose that activation of the boronic ester through a palladium–hydroxy species25 would facilitate transmetallation through a six‐membered transition state structure 9 26. This would lead to an allenyl palladium intermediate22c 10 , which after reductive elimination would give the all‐carbon tetrasubstituted allene 7 ab . Although the tetrasubstituted allenes prepared in Table 4 were either oils or solids which did not lead to crystals suitable for X‐ray crystallography, we were able to prepare a crystalline derivative that was suitable for analysis, which clearly shows the orientation of the four substituents around the allene moiety (Figure 1).…”

A regioselectivity switch in Pd-catalyzed hydroallylation of alkynes

“…Finally, the late-stage modification of the estrone derivative 1t affords 3t in 38% yield. This 1,5-diene synthesis complements known allyl–allyl couplings that require pre-functionalized allyl precursors such as allyl chlorides or carbonates 16,17…”

“…Instead, the isomerization product 1-phenyl-1,3-butadiene is observed for the conversion of 1p . Notably, substrates bearing pyridine rings, which were incompatible in previously reported palladium catalysis,16 also lead to 3r and 3s in moderate yields. Finally, the late-stage modification of the estrone derivative 1t affords 3t in 38% yield.…”

Catalytic intermolecular allyl–allyl cross-couplings between alcohols and boronates

“…Allyl boronates are typically used for addition to C(sp 2 ) centers. 12 Thus, our earlier report 10 represents the first use of these nontoxic reagents in C(sp 3 )-C(sp 3 ) crosscouplings. 11,13 More recently, Morken et al developed a palladium-catalysed asymmetric version with linear : branched ratios ranging from 1 : 3 to 1 : >20 (Scheme 1).…”

“…To address these problems we recently developed crosscouplings between primary or secondary allyl carbonates and allyl boronates [Scheme 1; B(pin) = pinacolatoboron]. 10 These reactions provided efficient access to various 1,5dienes 11 with linear : branched ratios ranging in most cases from 4 : 1 to >99 : 1. Allyl boronates are typically used for addition to C(sp 2 ) centers.…”