(4R,5R)-2-Bromo-1,3-bis[(4-methylphenyl)sulfonyl]-4,5-diphenyl-1,3,2-diazaborolidine

Abstract

[121758-17-6] C28H26BBrN2O4S2 (MW 609.36) InChI = 1S/C28H26BBrN2O4S2/c1-21-13-17-25(18-14-21)37(33,34)31-27(23-9-5-3-6-10-23)28(24-11-7-4-8-12-24)32(29(31)30)38(35,36)26-19-15-22(2)16-20-26/h3-20,27-28H,1-2H3/t27-,28-/m1/s1 InChIKey = PEEHKMHARMPWIU-VSGBNLITSA-N (chiral controller group for asymmetric carbonyl allylations,1-8 allenations,9 and propargylations,9 enantioselective Claisen rearrangements,10, 11 and enantioselective enolborinations12) Alternate Name: 2-bromo-4,5-diphenyl-1,3-bis-(toluene-4-sulfonyl)-[1,3,2]diazaborolidine. Solubility: soluble in dichloromethane. Form Supplied in: not commercially available. Preparative Methods: prepared from the corresponding bissulfonamide, (R,R)-1,2-diphenyl-1,2-diaminoethane-N,N′-bis(4-methylbenzenesulfonamide)13-16 and BBr3 in dichloromethane. After drying under high vacuum (0.1 mmHg) overnight (8–16 h) at 80–100 °C in a Schlenk flask, the sulfonamide (1.4 equiv) is dissolved in dichloromethane (0.1 M), and cooled to 0 °C. Care should be taken during drying, as temperatures above 100–110 °C produce a brownish-colored material which is insoluble in dichloromethane at 0.1 M and ineffective for chemical transformations. BBr3 (1.0 M in dichloromethane; 1.4 equiv) is added, the mixture is stirred at 0 °C for 10 min, warmed to room temperature, and stirred for 1 h. The solvent and HBr are then carefully removed under high vacuum, kept at room temperature under high vacuum for 15 min after all solvent has been removed, and the white to tan residue is then redissolved in dichloromethane (0.1 M). This evaporation–redissolution procedure is repeated two additional times, giving a 0.1 M solution of 1 in CH2Cl2 dichloromethane.7 Handling, Storage, and Precautions: highly moisture-sensitive; should be prepared immediately prior to use under inert atmosphere, preferably using standard Schlenk techniques (use of a glove box not required). Best results are obtained when fresh solutions of BBr3 are used.