Highly Enantioselective Reactions of α‐Sulfonyl Carbanions of Trifluoromethyl Sulfones

Abstract

Chirale Sulfone: Die katalytischen Umsetzungen von lithiiertem Benzyltrifluormethylsulfon mit Aldehyden verlaufen mit ausgezeichneter Diastereoselektivität und hoher Enantioselektivität. Auch die Fluorierung des Sulfons mit N‐Fluorbenzolsulfonimid in Gegenwart stöchiometrischer Mengen an Bis(oxazolinen) war außerordentlich enantioselektiv (bis 99 % ee).

Catalytic Conjugate Additions of Geminal Bis(sulfone)s: Expanding the Chemistry of Sulfones as Simple Alkyl Anion Equivalents

“…The reaction mixture was stirred at RT for 15 min. Afterwards, a further portion of InA C H T U N G T R E N N U N G (OTf) 3 (0.5 mol %) was added and the colorless solution was stirred for a further 15 min. The mixture was then passed through a short plug of neutral alumina which was washed with CH 2 Cl 2 .…”

“…[2] For years, realization of this concept has mainly relied on 1) irreversible generation of the sulfonyl a-carbanion by treatment with stoichiometric base in a separate step, 2) subsequent reaction with the corresponding electrophile; and 3) final reductive elimination of the sulfonyl group by action of metallic sodium or magnesium. [1][2][3] Although more advanced, direct methods capable of merging steps (1) and (2) by means of catalytic activation of the substrates still remain challenging. To date, sulfone-based direct catalytic C-C bond-forming methods are confined to either a-fluoro bis(phenylsulfonyl)methane [4] or monosulfones bearing an additional carbonyl, ester, or nitrile group at the a-position (Scheme 1).…”

Chiral Fluorinated α‐Sulfonyl Carbanions: Enantioselective Synthesis and Electrophilic Capture, Racemization Dynamics, and Structure

“…According to natural bond orbital (NBO) calculations of [R 1 C(R 2 )SO 2 R] À (R = tBu, CF 3 ) the n C !s* SÀR interaction is much stronger for R = CF 3 3 ]-A C H T U N G T R E N N U N G NBu 4 predominantly form monomers in tetrahydrofuran (THF) at À108 8C. [14] Results and Discussion Synthesis of achiral and racemic (S)-trifluoromethyl-and (S)-nonafluorobutylsulfones: Because of our previous studies of the (S)-tert-butylsulfonyl carbanion salts Ia-d, [3,4] we selected the (S)-trifluoromethylsulfonyl carbanion salts 1, 2, 3 a-d, 4, and 5 ( Figure 2) for the determination of 1) the configurational stability of salts of type II and its dependence on the counterion and substituents at the C a atom, and 2) the study of the enantioselective synthesis and electrophilic capture of II. Keywords: ab initio calculations · carbanions · chirality · racemization · sulfone meric O À Li contact ion pairs (CIPs) in solution in tetrahydrofuran (THF) and in the crystal phase.…”

“…Thermodynamic parameters of the enantiomerization of the benzylic lithium a-sulfonyl carbanion salt rac-3 a and benzylic tetrabutylammonium a-sulfonyl carbanion salt rac-3 b in THF. [14] Thus, it is proposed that triflone (S)-12 also reacts with the lithiumorganyl by means of a prior reversible coordination to one of the O atoms with formation of the corresponding diastereomeric complexes (S,S S )-12·RLi and (S,R S )-12·RLi (Scheme 16). [14] Thus, it is proposed that triflone (S)-12 also reacts with the lithiumorganyl by means of a prior reversible coordination to one of the O atoms with formation of the corresponding diastereomeric complexes (S,S S )-12·RLi and (S,R S )-12·RLi (Scheme 16).…”

Catalytic and Highly Enantioselective Reactions of α‐Sulfonyl Carbanions with Chiral Bis(oxazoline)s

“…Recently, we communicated the first highly enantioselective reactions of a-lithiated sulfones with various electrophiles by using a stoichiometric or a substoichiometric amount of a chiral bis(oxazoline). [8,9] Herein, we focus on a detailed study of the enantioselective reactions of a-lithiated sulfones and a systematic study of this type of asymmetric synthesis.…”