Silicon in organic synthesis. 27. A method for the generation of electronegatively substituted cyclopropyl anions under preparatively useful conditions. Aldol condensation with carbonyl partners

Chemical reactivity and configurational properties of cyclopropyl carbanions derived from a silyl sulfonyl substituted cyclopropene

“…(49) For some related reactions of cyclopropanes carrying sulfonyl groups, see ref 31, 32. (50) For an interesting discussion concerning intramolecular solvation of lithium by oxygen in lithiated enol ethers, see: Lau, K. S. Y.; Schlosser, completely to the E-methoxy lithiate 29, even at -90 °C. Thus, reaction of 24 with n-butyllithium (1 min, -70 °C) followed by D20 quenching gave 25, whereas reaction with methyl iodide and cyclohexanone afforded 26 and 27, identical with samples prepared from the E-olefin 23. This rapid Z -* E isomerization may be facilitated by reduced double-bond order in a "push-pull" olefin such as 23 (or 24) and is quite analogous to the situation found for 2methoxy-l-(p-toluenesulfonyl)cyclopropyl carbanion 17 where stabilization of the E isomer was attributed to lithium chelation by the ß-methoxy substituent.…”

“…No signs of the vinyl signal at 5.70 could be detected in the crude NMR spectrum. Quenching of the above carbanion derived from 23 and 24 with methyl iodide gave (E)-2-methoxy-l-methyl-l-(phenylsulfonyl)ethylene ( 26) in 98% as a clear oil: IR (neat) 3060, 2940, 2840, 1650, 1445,1300,1245,1140, 1080, 960, 780, 760, and 690 cm"1; NMR (CDC13, 300 MHz) 1.71 (s, 3 H), 3.87 (s, 3 H), 7.35 (s, 1 H), 7.4-7.65 (m, 3 H), and 7.S-7.9 (m, 2 H); MS, m/e 212 (M+), 125, 84 (base), and 77% HRMS caled for C10H12O3S 212.0507, found 212.0482.…”

Catalytic and Photochemical Cyclopropanation of Alkenes with Methyl Diazo(trialkylsilyl)acetates: Steric Effects and Thermodynamic Stabilities of Cyclopropanes

“…Since the catalytic reactions yield cyclopropanes 2a − f with a preference for the diastereomer which has the ester group in a position cis to the vicinal ring substituents R 1 , a desilylation reaction with retention of configuration would produce the thermodynamically less stable cis -cyclopropanecarboxylate as the major diastereomer . This approach would be stereocomplementary to the direct cyclopropanation of the same alkenes with unsubstituted diazoacetic esters.…”

Tetra-n-butylammonium Fluoride

“…Fluoride can induce C-N and C-S bond formation in reactions of organosilanes with nitrogen-or sulfur-containing electrophiles such as imines, nitriles, nitro compounds, or sulfines, or by oxidative coupling of organosilanes with nitrogen or sulfur nucleophiles. (50) Polyfluoroalkoxylation of aromatic rings has been achieved by S N Ar reactions of dinitrobenzenes with polyfluoro alcohols in the presence of excess TBAF (eq 51). 120 Allyl and benzyl sulfoxides were prepared from sulfines by fluoride-induced C-S coupling (eq 43).…”