Inverse Amine‐Stabilized Sulfenes F₂CSO₂ and FHCSO₂

Abstract

rnate.I4] The Grignard reagent 3 consists of an equilibrium mixture of enantiomers, diastereomers, and conformational isomers owing to rotation around formal single bondsrs] and 1,3-metallotropic shift.[61 Borate 4 reacts preferentially with 3 b, brr7] to afford an 89 % yield of the pentenylboronic esters 1 and 5, which have (Z) configurations (cf. Ref. [S]). v 5 Furthermore, the chiral borate 4 differentiates between the enantiomers 3b,b', so that 1 can be obtained with a diastereomeric excess of 94 % by kinetic resolution of a racemate. This was established by reaction of 1 with benzaldehyde and determination of the enantiomeric purity of alcohol 2. The glycol from which 4 is derived and thus the reagent 1 are readily accessible in either enantiomeric Experimental ProcedureA 0.85 M solution (6.0 mL, 5.1 mmol) of (1-methyl-2-buteny1)magnesium chloride (3) in THF was added dropwise over 15 min to a solution of (4S,5s)-2-isopropyloxy-4,5-dicyclohexyl-1,3,2-dioxaborolane (4; prepared from 1,2-dicycIohexylethane-l,2-diol and triisopropyl borate by distillative removal of the isopropanol) in 20 mL of THF at -78 "C. The solution was allowed to warm overnight to room temperature and the products were hydrolyzed by addition of a saturated solution (1 5 mL) of NH,CI. The aqueous phase was extracted with 3 x 20 mL of ether and the organic phase was dried over MgSO, and concentrated. The colorless oily residue was chromatographed with CH,Cl, (column 30 x 2 cm, silica gel 60), affording 1.38 g (89 YO) of boronic ester 1. For spectroscopic data and determination of the enantiomeric purity by addition to benzaldehyde, see 12). 0 VCH Verlagsgesellschaft mbH, 0-6940 Wemherm, 1990 0570-0833190~0lOl-0061 $ 0 2 SO10

Difluoromethylation of Amines with Zn(CF3)Br · 2 CH3CN, Cd(CF3)2 · 2 CH3CN and the System Bi(CF3)3/AlCl3

“…Elemental analysis for C 4 (Difluoromethyl)triethylammonium bromide. The compound was obtained by the method described above from 2.96 g (10.0 mmol) Zn(CF 3 )Br´2 CH 3 CN and 2.02 g (20.0 mmol) triethylamine in 54% yield (1.25 g).…”

“…(Difluoromethyl)trialkylammonium salts were prepared either by reactions of (CH 3 ) 3 SnCF 3 with tertiary amines in the presence of boron halides [2], by reactions of the system CBr 2 F 2 /Zn or Mg [3] or by hydrolysis of the tertiary amine stabilized sulfene, CF 2 =SO 2 [4].…”

Sulfonyl esters 7. The second and third sequences in the Trithioorthoformate Reaction

“…[13]). However, the Trithioorthoformate Reaction completely consumes added NaH to produce carbanions and sulfenylated sulfonate esters.…”

“…Sulfonic acid esters are well-established presursors for the formation of sulfenes (1,12). Attack by mercaptide anions at the sulfene carbon (Scheme 6) is known as "carbophilic" attack (1 1) and has ample precedent (13). PM3 computations on CH,SO, show it to have a near-degenerate pair of vacant frontier orbitals (Fig.…”