Transformation of Aldehydes into (E)-1-Alkenylsilanes and (E)-1-Alkenylboronic Esters with a Catalytic Amount of a Chromium Salt

Abstract

(Diiodomethyl)trimethylsilane (Me3SiCHI2, 1) is produced by treatment of iodoform with manganese in the presence of Me3SiCl. Aldehydes are converted to (E)-1-trimethylsilyl-1-alkenes in a stereoselective manner with a geminal dichromium reagent generated from 1, manganese, Me3SiCl, and a catalytic amount of CrCl3[thf]3 in THF. Similarly, (E)-1-alkenylboronic esters are prepared stereoselectively in good to excellent yields by treatment of aldehydes with a geminal dichromium reagent derived from Cl2CHB(OR)2 [(OR)2 = OCMe2CMe2O] and LiI instead of 1.

Total Synthesis of Marinomycin A Based on a Direct Dimerization Strategy

“…Mitsunobu inversion [18] of the C25 hydroxy group afforded 4-nitrobenzoate 25, which, upon selective desilylation [19] and methanolytic removal of the 4-nitrobenzoyl group, delivered diol 27 via 26 in good yield. After TEMPO oxidation of 27, the resulting aldehyde was directly subjected to Takai olefination with pinacol (dichloromethyl)boronate [10] to stereoselectively produce E-boronate 6. Without purification, boronate 6 was then coupled to the aromatic fragment 5 under Suzuki-Miyaura reaction conditions to furnish the required monomeric hydroxy salicylate 4 in 48 % overall yield from 27.…”

“…Fragment 6 was considered to be accessible from alkyne 7 and epoxide 8 through an acetyleneepoxide coupling, [9] inversion of the C25 stereochemistry, and Takai olefination. [10] Both alkyne 7 and epoxide 8 would in turn be derived from the readily available 1,3-diol chiral building block 9 through a method we have previously developed. [11] The synthesis of alkyne 7 commenced with the four-step preparation of enantiopure acetonide 9 from s-symmetrical dialkenyl carbinol 10 in a sequence involving a Katsuki-Sharpless asymmetric epoxidation, [12] Mitsunobu inversion, Red-Al reduction of an epoxy alcohol with concomitant loss of a benzyloxy group as in 14, and acetonide formation,…”

Total Synthesis of Marinomycin A Based on a Direct Dimerization Strategy

“…Mitsunobu inversion [18] of the C25 hydroxy group afforded 4-nitrobenzoate 25, which, upon selective desilylation [19] and methanolytic removal of the 4-nitrobenzoyl group, delivered diol 27 via 26 in good yield. After TEMPO oxidation of 27, the resulting aldehyde was directly subjected to Takai olefination with pinacol (dichloromethyl)boronate [10] to stereoselectively produce E-boronate 6. Without purification, boronate 6 was then coupled to the aromatic fragment 5 under Suzuki-Miyaura reaction conditions to furnish the required monomeric hydroxy salicylate 4 in 48 % overall yield from 27.…”

“…Fragment 6 was considered to be accessible from alkyne 7 and epoxide 8 through an acetyleneepoxide coupling, [9] inversion of the C25 stereochemistry, and Takai olefination. [10] Both alkyne 7 and epoxide 8 would in turn be derived from the readily available 1,3-diol chiral building block 9 through a method we have previously developed. [11] The synthesis of alkyne 7 commenced with the four-step preparation of enantiopure acetonide 9 from s-symmetrical dialkenyl carbinol 10 in a sequence involving a KatsukiSharpless asymmetric epoxidation, [12] Mitsunobu inversion, Red-Al reduction of an epoxy alcohol with concomitant loss of a benzyloxy group as in 14, and acetonide formation, according to our established procedure [11] (Scheme 2).…”

Synthesis of Vinylsilanes

“…Since the original report, the Takai group has developed a variant which is catalytic in chromium, employing manganese as a stoichiometric reductant. 26 For simple aldehydes, this procedure maintains the high stereoselectivity of the transformation (entries 5-8).…”