“Design” of Boron‐Based Compounds as Pro‐Nucleophiles and Co‐Catalysts for Indium(I)‐Catalyzed Allyl Transfer to Various Csp³‐Type Electrophiles

Abstract

We have recently uncovered a general indium(I)-catalyzed method for allylations and propargylation of acetals and ketals with a water- and air-stable allyl boronate. By using a more reactive allyl borane, we have successfully extended this methodology to the more challenging C-C coupling with ethers. Herein, we report an improved methodology for the indium(I)-catalyzed allylation of acetals and ethers, through combination of the allyl boronate with a commercially available "hard" Lewis acid, B-methoxy-9-BBN (BBN=borabicyclo[3.3.1]nonane), as an effective co-catalyst. Significantly, our work highlights for the first time the correlation between the Lewis acidity of "electrophilic" boron-based compounds and their "nucleophilic" reactivity in Csp(3)-Csp(3) couplings, catalyzed by a "soft" low-oxidation main group metal. In addition, we also report several applications of these methodologies to the selective synthesis of various carbohydrate derivatives.

Recent Developments in the Ferrier Rearrangement

“…Related [1→3]‐alkoxy shifts have also been observed in 3,4,6‐tri‐ O ‐benzyl glycals 17,26. It has thus been shown that per‐ O ‐benzyl‐ D ‐glycals are prone to undergo allylic transposition in the presence of Montmorillonite K‐10 as catalyst.…”

“…Kobayashi and co‐workers have recently described the use of boron‐based compounds as pro‐nucleophiles and co‐catalysts for indium‐(I)‐catalyzed allyl and propargyl transfer to Csp 3 ‐type electrophiles, and this was applied to allyl and propargyl Ferrier‐type transfer to glycals 26,204. Allyl boronate 214a (Scheme , a) thus reacted with tri‐ O ‐acetyl‐ D ‐glucal ( 5 ) in the presence of InOTf in CH 2 Cl 2 at room temperature to give C ‐glycoside 185 .…”

Boron-based pronucleophiles in catalytic (asymmetric) C(sp3)–allyl cross-couplings

“…Importantly, our concept employing borane 16, rather than boronate 2 [22], proved to be applicable to carbohydrate chemistry, as demonstrated by the conversion 17 → 18 (Scheme 7) [23].…”

“…Initial metal screening for the reaction of N,O-aminal rac-4a with boronate 2 identified In(I) as the best catalyst (R = Ph, PG = Bz, R' = Me; Scheme 9) [21]. On the other hand, the corresponding Hosomi-Sakurai allylation [23] with silicon-based reagents 19 hardly proceeded. The substantially higher reactivity of 2 over 19 under mild conditions constitutes a prerequisite for asymmetric catalysis.…”

Transformation of Carbonyl Compounds into Homologous Alkynes under Neutral Conditions: Fragmentation of Tetrazoles Derived from Cyanophosphates

“…By the same procedure as used for the preparation of 21 , aldehyde 2e (223 mg, 0.5 mmol) provided a 9:1 mixture (138 mg, 62%) of β-9e and α-9e after purification by silica gel column chromatography (EtOAc:hexane, 1:9).…”