Synthetic Methodology for the Construction of Structurally Diverse Cyclopropanes

Abstract

diastereoselective syntheses, enantioselective syntheses diastereoselective syntheses, enantioselective syntheses (incl. cis/trans-isomerism) O 0031 -034Synthetic Methodology for the Construction of Structurally Diverse Cyclopropanes.-Practical and efficient routes for the stereoselective conversion of homoallylic alcohols like (I) and (VII) to diastereomerically pure cis-and trans-1,2-disubstituted, and 1,2,3-trisubstituted cyclopropanes are developed. One route involves ring closing metathesis reaction of bisolefins like (III) to give after cleavage of the 7-membered ring the silylated cyclization precursors like (V). The other more efficient approach provides the cyclopropanes in just two steps by cross-metathesis reaction of the homoallylic alcohol and by activation of the cyclization precursors like (XV) with inexpensive SOCl 2 at room temperature. The cyclopropane product chirality is ultimatively controlled by the choice of homoallylic alcohol starting material.

Fluorine‐Directed Diastereoselective Iodocyclizations

“…[4,5] The synthesis of 1 h and 1 i was more challenging and relied on a multistep ring-closing metathesis and ring-opening approach to access the allylsilanes required for subsequent electrophilic fluorinations. [5,6] The synthesis of the allylic fluorides (AE )-1 g and (AE )-1 h is shown in Scheme 1.…”

Modular Terpenoid Construction via Catalytic Enantioselective Formation of All-Carbon Quaternary Centers: Total Synthesis of Oridamycin A, Triptoquinones B and C, and Isoiresin

“…For isoiresin, Diels-Alder cycloaddition with iso -Fragment A and dimethyl acetylene dicarboxylate represents an alternative to Friedel-Crafts cyclization. Fragment A , the common intermediate en route to each natural product, is prepared in 4 steps through anti -diastereo- and enantioselective tert -(hydroxy)prenylation 5 of commercially available alcohol 1 followed by ring-closing metathesis 12 and intramolecular Sakurai allylation. 13 Sakurai allylation, when conducted under more forcing conditions, converts Fragment A to iso -Fragment A .…”

Metal free fluoroamination of allylsilanes: A route to 3-fluoropyrrolidines

“…13 C NMR spectra were recorded in deuterated solvents using Bruker DPX200, DPX400, AV400 and AV500 spectrometers, calibrated using residual undeuterated solvent as an internal reference. 19 F spectra were recorded on an AV400 spectrometer, calibrated using fluorotrichloromethane (CFCl 3 ) as a reference.…”

“…Compounds (Z)-1a, (Z)-1b and (Z)-1g were prepared by substituting the corresponding activated alcohols with tosyl amine in DMF. The Z geometry of all precursors was secured through a key ring closing metathesis as previously reported in the literature [8,13,14]. The preparation of (E)-1h began with the known (E)-2,2-dimethyl-5-(triisopropylsilyl)pent-3-enoic acid [8].…”