Stereoselective Cyclopropanation Reactions

Abstract

25 with the reagent derived from 1,1-diiodoethane and diethylzinc (eq 12). 43,44 The level of induction was highly dependent on the nature of the nitrogen protecting group.An interesting cyclopropanation of an exocyclic olefin was reported by Ronald (eq 13). 45 The cyclopropanation of 2-methylenecyclohexanol using 13 Table 4. Cyclopropanation of (E)-3-Penten-2-ol 47 conditions ratio 31:32

Catalytic Asymmetric Generation of (Z)-Disubstituted Allylic Alcohols

“…1-4 They are also precursors to enantioenriched epoxy alcohols, 5-7,4,1,8-10 allylic amines, 11-14 α-and β-amino acids, 13,15 and cyclopropyl alcohols. [16][17][18][19] Enantioenriched allylic alcohols are often isolated from kinetic resolution (KR) with the Sharpless-Katsuki asymmetric epoxidation catalyst. [5][6][7]4 Although (E)-allylic alcohols are excellent substrates for the KR, (Z)-disubstituted allylic alcohols are not (Scheme 1).…”

Formal Total Synthesis of (−)-Jiadifenolide and Synthetic Studies toward seco-Prezizaane-Type Sesquiterpenes

“…The next challenge was to find an appropriate reducing agent for the transformation of the methylester 12 to the corresponding aldehyde, and to install the D-ring later. The use of LiAlH 4 proved to be too harsh as several products were detected by NMR analysis of the reaction mixture after work-up, whereas reaction with NaBH 4 in ethanol at 60 °C and superhydride (LiEt 3 BH) in THF at 0 °C selectively reduced the lactone moiety, while the Additionally, were tested on the diol 16, but even with the allylic hydroxy group serving as a directing group, 21 we were not able to cyclopropanate the butenolide moiety.…”

Functionalisation of Macroheterocycles with Preserving and Changing Their Sizes

“…For example, the cyclopropanation reaction is applicable in case of enantiomeric pure R-muscone (49) that is an odorous substance (muscus) isolated from glands of musk deer Moschus moschiferus. [46,47] Asymmetrically catalysed cyclization of 14-pentadecinal (50) consisting in hydroboration of its triple bond followed by transmetalation and interaction with the aldehyde functional group in the presence of (-)-3-exo-(dimethylamino) isoborneol (51) yielded E-allyl alcohol (52) with high (92% ee) enantiomeric purity. Hydroxy-directed cyclopropnation by the Denmark method followed by recrystallization yielded the sole diasterereomer of alcohol (53), the Swern oxidation of which and reduction of the cyclopropyl functional group completed the synthesis (Scheme 15).…”

“…This approach has been successfully carried out upon the action of metachloroperbenzoic acid on olefins in synthesis of ionophor units [48,49] and representatives of a very large family of chemically bound mycotoxins (trichothecins) [50] of the cyclam ring and low solubility of the ion pair formed by the macrocyclic cation and iodide ion (Scheme 13). [45] Two-step synthesis of mono-N-substituted cyclen (47) with the carbamide side chain consisting in direct functionalization of cyclen (31) up to trisubstituted derivative (48) and its treatment with butyl isocyanate (Scheme 14) is an illustration of correlations between mono-and trisubstituted azacrowns. [40] The literature describes numerous examples of synthesis, in which additional fragments to the already prepared Macroheterocycles Functionalization Accompanied by Preservation and Changing Their Size dioxirane (DMDO) in synthesis of epothilone A and B, [51] their analogues, [52] and antibiotic erythromycin derivatives A.…”

“…Introducing diisocyanate (138) into condensation allows "stitching" two cyclen (48) molecules with dicarbamide spacer in compound (139). The resulting cyclen derivatives (38), (47) and (139) ions (Scheme 32). [91] Monoalkylation of trisubstituted cyclen (42b) and cyclam (43b) allows introducing such substituents as xylyl groups.…”