2007
DOI: 10.1021/jo701833v
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Diastereoselective Construction of Quaternary Carbons Directed via Macrocyclic Ring Conformation:  Formal Synthesis of (−)-Mesembrine

Abstract: In this article, we report a highly diastereoselective new method for the generation of quaternary carbon centers through an anionic oxy-Cope/alkylation sequence where the diastereoselectivity is induced by the conformation of a macrocyclic tetrasubstituted enolate. The use of our methodology culminated in the formal total synthesis of (-)-mesembrine (34) in 11 steps from known starting materials.

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Cited by 32 publications
(7 citation statements)
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“…1 H and 13 C NMR spectra of epoxide 16 were consistent with the structure shown, where epoxidation took place only at the 9,10-alkene, located away from carbohydrate fused region of the macrolide 8. However, at this point the reason behind the observed regioselectivity in the epoxidation of 8 is not fully apparent.As observed earlier for other[13]-macrodilactones and[15]-macrodilactones, facial selectivities of the alkene and diene units originated via macrocyclic diastereocontrol[36][37][38][39][40]. Being present in a rigid cyclic structure, the planar 1,3-diene unit in macrocycle 8 was not able to rotate around its own axis.…”
mentioning
confidence: 62%
See 1 more Smart Citation
“…1 H and 13 C NMR spectra of epoxide 16 were consistent with the structure shown, where epoxidation took place only at the 9,10-alkene, located away from carbohydrate fused region of the macrolide 8. However, at this point the reason behind the observed regioselectivity in the epoxidation of 8 is not fully apparent.As observed earlier for other[13]-macrodilactones and[15]-macrodilactones, facial selectivities of the alkene and diene units originated via macrocyclic diastereocontrol[36][37][38][39][40]. Being present in a rigid cyclic structure, the planar 1,3-diene unit in macrocycle 8 was not able to rotate around its own axis.…”
mentioning
confidence: 62%
“…On the basis of all the above observations,[15]-macrodilactone 8 displayed a narrow, elongated, and rigid structure compared to macrodilactone 7. Perhaps it was because of the rigidity of the overall system that macrocyclic ring closure became comparatively more difficult and it reflected in the lower yield of the intramolecular Stille coupling for[15]macrodilactone 8 compared to its non-sugar analogs.2.3 Regio-and diastereoselective epoxidation of the macrocyclic diene unitAnalogous to 7, however, glucose-fused macrocycle 8 was found to expose only one face of its diene to the outer environment[36][37][38][39][40]. Macrocycle 8 positioned the opposite face of the diene outward even though the configuration at C2 (that in 7 was the key center controlling the planar chirality) was the same in both the macrocycles.…”
mentioning
confidence: 99%
“…Silyl enol ether 25 a was isolated in 15 % yield along with 75 % of the unreacted starting material 24 a. [4] A series of NOE signals established a trans relationship between the OTMS and phenyl groups as shown, as well as the orientation of the trisubstituted double bond. In contrast, when the anionic oxy-Cope of 7 a was quenched with TMSCl, the macrocycle 26 a was found to have a cis geometry between the OTMS and phenyl groups.…”
Section: Wwwchemeurjorgmentioning
confidence: 85%
“…(2)]. Under anionic conditions, oxy‐Cope rearrangement of 7 a 4 followed by the addition of E–X afforded macrocycles 13 a and 13 aa which upon heating led to 17 a and 17 aa respectively as the sole observable isomers [Eq. (3)].…”
Section: Introductionmentioning
confidence: 99%
“…The planar chirality of the ring, therefore, controls the diastereoselectivity of epoxidation of the [13]-macrodilactones, which is an example of macrocyclic diastereocontrol. [30] Macrocycles 6 and 7 were both epoxidized under established reaction conditions that involved either in situ generation of dimethyl dioxirane( DMDO) in the presence of the substrate or addition of as olution of DMDO to as olution of the substrate. [10,31] When a-substituted [13]-macrodilactone 6 was the substrate, two diastereomerice poxides, 9 and 10 (Figure 4), were obtained in aratio of approximately 1:3.…”
Section: Macrocyclic Diastereocontrol As Ar Eadoutofs Olution Conformmentioning
confidence: 99%