Concave Reagents. 20. Sterically Shielded m-Terphenyls as Selective Agents in General Protonations¹

Abstract

New m-terphenyls with acidic substituents in the 2'-position have been used in general protonations leading to reagent-controlled selectivity enhancements: up to 96:4 for the gamma/alpha-protonation of unsymmetrically substituted allyl anions, up to 97:3 for the protonation of cyclohexyl anions generating preferentially the thermodynamically less stable cis-products. In order to allow a general, reagent-controlled protonation the acidity of the protonating agent should be as low as possible.

Asymmetric Synthesis of Diverse Glycolic Acid Scaffolds via Dynamic Kinetic Resolution of α-Keto Esters

“…Because less sterically encumbering sulfonamides ( L9 – L12 ) resulted in erosions in selectivity, we sought to synthesize bulkier sulfonamides by exploring new chiral space at the 2,6-positions of the arylsulfonamide . A number of diverse sulfonyl chlorides were synthesized through a one-pot double alkylation/sulfonylation of 1,3-dichlorobenzene . The simplest m -terphenyl sulfonamide variant L14 distinguished itself as being uniquely effective for providing high levels of enantioselectivity for the title reaction (95:5 er).…”

Synthesis of Bis(phosphine) and N-Heterocyclic Carbene Supported α- Diazoalkyl Complexes of Copper(I)

“…The preparation followed standard synthetic protocols, except that longer reaction times and higher temperatures were required compared with the reaction conditions for smaller aryl derivatives (e.g., N 2 CHPh) . Following a procedure for a related compound, monolithiation of (dmp)I in cyclohexane followed by addition of N , N -dimethylformamide allowed for the isolation of (dmp)CHO in 70% yield. Hydrazine condensation with the aldehyde gave (dmp)CHN 2 H 2 (93% yield), and oxidation of the hydrazone with an excess of HgO gave 1 as a light salmon colored solid in 82% yield.…”

First Total Synthesis of (±)-Melinonine-E and (±)-Strychnoxanthine Using a Radical Cyclization Process as the Core Ring-Forming Step

“…A mixture of pentacyclic nitriles 19 and 20 (2:3 ratio), the latter with the natural relative stereochemistry at C-20, was obtained . It is worth mentioning that the major epimer 20 arises from the equatorial protonation of the exocyclic α-cyano carbanion to leave an axial cyano substituent …”