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Asymmetric syntheses of the following 17‐membered macrocyclic spermine alkaloids are presented: (−)‐(S)‐protoverbine (=(8S)‐8‐phenyl‐1,5,9,13‐tetraazacycloheptadecane‐6‐one; 1 ), (+)‐(S)‐protomethine (=(2S)‐2‐phenyl‐1,5,9,14‐tetraazabicyclo[12.3.1]octadecan‐4‐one; 2 ), (−)‐(S)‐buchnerine (=(8S)‐8‐(4‐methoxyphenyl)‐1,5,9,13‐tetraazacycloheptadecane‐6‐one; 8 ), (+)‐(S)‐verbamethine (=(+)‐(2S)‐9‐[(E)‐phenylprop‐2‐enoyl]‐2‐phenyl‐1,5,9,14‐tetraazabicyclo[12.3.1]octadecan‐4‐one; 4 ), (−)‐(S)‐verbacine (=(−)‐(8S)‐1‐[(E)‐phenylprop‐2‐enoyl]‐8‐phenyl‐1,5,9,13‐tetraazacycloheptadecan‐6‐one; 3 ), (−)‐(S)‐verbasikrine (=(−)‐(8S)‐1‐[(E)‐3‐(4‐methoxyphenyl)prop‐2‐enoyl]‐8‐phenyl‐1,5,9,13‐tetraazacycloheptadecan‐6‐one; 26 ), (−)‐(S)‐isoverbasikrine (=(−)‐(8S)‐1‐[(Z)‐3‐(4‐methoxyphenyl)prop‐2‐enoyl]‐8‐phenyl‐1,5,9,13‐tetraazacycloheptadecan‐6‐one; 25 ), (+)‐(S)‐verbamekrine (=(+)‐(2S)‐9‐[(E)‐3‐(4‐methoxyphenyl)prop‐2‐enoyl]‐2‐phenyl‐1,5,9,14‐tetraazabicyclo[12.3.1]octadecan‐4‐one; 23 ), and (+)‐(S)‐isoverbamekrine (=(+)‐(2S)‐9‐[(Z)‐3‐(4‐methoxyphenyl)prop‐2‐enoyl]‐2‐phenyl‐1,5,9,14‐tetraazabicyclo[12.3.1]octadecan‐4‐one; 24 ). Effective methods for 1H‐NMR determination of the enantiomeric purity in which (S)‐2‐hydroxy‐2‐phenylacetic acid and (S)‐2‐acetoxy‐2‐phenylacetic acid are used as shift reagents for 1, 8 , and related macrocyclic alkaloids are described.  相似文献   

3.
Strictamine and rhazinoline are representative methanoquinolizidine‐containing akuammiline alkaloids that possess different stereochemistry at the C16 position. A unified approach to the enantioselective total syntheses of these two molecules is described. The key steps in this synthesis include a photocatalytic intra/intermolecular type II radical cascade reaction, a Tsuji–Trost allylation, a palladium‐ or nickel‐mediated cyclization, and a late‐stage intramolecular N‐alkylation reaction.  相似文献   

4.
The total syntheses of four fawcettimine‐related Lycopodium alkaloids, (±)‐fawcettimine, (±)‐fawcettidine, (±)‐lycoposerramine‐Q, and (±)‐lycoflexine, were completed in a highly stereoselective manner. The Pauson–Khand reaction of 4‐methylidene‐6‐siloxyoct‐1‐en‐7‐yne followed by regio‐ and stereoselective hydrogenation led to the short‐step preparation of the bicyclo[4.3.0]nonenone intermediate bearing a methyl group with the required stereochemistry. The subsequent chemical manipulation of the bicyclic compound afforded the 6‐5‐9‐membered tricyclic dioxo compound, which was then transformed into the four targeted alkaloids in an alternative and more efficient fashion.  相似文献   

5.
The syntheses of four macrocyclic spermine alkaloids, (±)‐budmunchiamine A – C ( 1a – c ) and (±)‐budmunchiamine L4 ( 1 ), were accomplished by Michael addition of spermine to the α,β‐unsaturated esters 3a – d , followed by cyclization of the resulting α,ω‐tetraamino esters 4a – d with triethoxyantimony; N‐methylation of the amino lactams 6a – c yielded the budmunchiamines A – C ( 1a – c ).  相似文献   

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The total syntheses of medicarpin, sophoracarpan A, and kushecarpin A from a common intermediate are achieved by using ortho and para‐quinone methide chemistry. Additionally, the relative stereochemistry of sophoracarpan A and B have been reassigned.  相似文献   

10.
Cyclopianes are novel diterpenes featuring a highly strained 6/5/5/5 tetracyclic core embedded with 6–8 consecutive stereocenters. The concise total syntheses of (?)‐conidiogenone B, (?)‐conidiogenone, and (?)‐conidiogenol have been accomplished in 14–17 steps. The present work features a HAT‐mediated alkene–nitrile cyclization to access the cis‐biquinane, a Nicholas/Pauson–Khand reaction to construct the linear triquinane, and a Danheiser annulation to afford the congested angular triquinane skeleton.  相似文献   

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The total syntheses of medicarpin, sophoracarpan A, and kushecarpin A from a common intermediate are achieved by using ortho and para‐quinone methide chemistry. Additionally, the relative stereochemistry of sophoracarpan A and B have been reassigned.  相似文献   

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Divergent total syntheses of the enmein‐type natural products (−)‐enmein, (−)‐isodocarpin, and (−)‐sculponin R have been achieved in a concise fashion. Key features of the strategy include 1) an efficient early‐stage cage formation to control succeeding diastereoselectivity, 2) a one‐pot acylation/akylation/lactonization to construct the C‐ring and C8 quarternary center, 3) a reductive alkenylation approach to construct the enmain D/E rings and 4) a flexible route to allow divergent syntheses of three natural products.  相似文献   

13.
The first total syntheses of the architecturally complex atisane‐type diterpenes and biogenetically related atisine‐type diterpenoid alkaloids (±)‐spiramilactone B, (±)‐spiraminol, (±)‐dihydroajaconine, and (±)‐spiramines C and D are reported. Highlights of the synthesis include a late‐stage biomimetic transformation of spiramilactone B, a facile formal lactone migration from the pentacyclic skeleton of spiramilactone E, a highly efficient and diastereoselective 1,7‐enyne cycloisomerization to construct the functionalized tetracyclic atisane skeleton, and a tandem retro‐Diels–Alder/intramolecular Diels–Alder sequence to achieve the tricyclo[6.2.2.0] ring system.  相似文献   

14.
The first total syntheses of the architecturally complex atisane‐type diterpenes and biogenetically related atisine‐type diterpenoid alkaloids (±)‐spiramilactone B, (±)‐spiraminol, (±)‐dihydroajaconine, and (±)‐spiramines C and D are reported. Highlights of the synthesis include a late‐stage biomimetic transformation of spiramilactone B, a facile formal lactone migration from the pentacyclic skeleton of spiramilactone E, a highly efficient and diastereoselective 1,7‐enyne cycloisomerization to construct the functionalized tetracyclic atisane skeleton, and a tandem retro‐Diels–Alder/intramolecular Diels–Alder sequence to achieve the tricyclo[6.2.2.0] ring system.  相似文献   

15.
A simple and efficient enantioselective synthesis of chromene, (?)‐(R)‐cordiachromene ( 1 ), and (?)‐(R)‐dictyochromenol ( 2 ) has been accomplished. This convergent synthesis utilizes intramolecular SNAr reaction for the formation of chroman ring, and Seebach's method of ‘self‐reproduction of chirality’ should establish the (R)‐configuration of the C(2) side chain as key steps.  相似文献   

16.
Divergent total syntheses of the enmein‐type natural products (?)‐enmein, (?)‐isodocarpin, and (?)‐sculponin R have been achieved in a concise fashion. Key features of the strategy include 1) an efficient early‐stage cage formation to control succeeding diastereoselectivity, 2) a one‐pot acylation/akylation/lactonization to construct the C‐ring and C8 quarternary center, 3) a reductive alkenylation approach to construct the enmain D/E rings and 4) a flexible route to allow divergent syntheses of three natural products.  相似文献   

17.
Total syntheses of the monoterpenoid indole alkaloids (±)‐alstoscholarisine B and C were accomplished starting from a readily available indole‐2‐acetic ester and an α,β‐unsaturated N ‐sulfonyllactam.  相似文献   

18.
The first chemical syntheses of complex, bis‐Strychnos alkaloids (?)‐sungucine ( 1 ), (?)‐isosungucine ( 2 ), and (?)‐strychnogucine B ( 3 ) from (?)‐strychnine ( 4 ) is reported. Key steps included (1) the Polonovski–Potier activation of strychnine N‐oxide; (2) a biomimetic Mannich coupling to forge the signature C23?C5′ bond that joins two monoterpene indole monomers; and (3) a sequential HBr/NaBH3CN‐mediated reduction to fashion the ethylidene moieties in 1 – 3 . DFT calculations were employed to rationalize the regiochemical course of reactions involving strychnine congeners.  相似文献   

19.
Total syntheses of (?)‐isoschizogamine and (?)‐2‐hydroxyisoschizogamine are described. The synthesis employs two asymmetric Michael additions to establish chiral centers at C7 and the quaternary carbon C20. Regioselective reduction of the methylthioiminium cation rather than the enamine generates an isoschizogamine‐type pentacyclic skeleton. Acidic hydrolysis of the isoschizogamine‐type intermediate in the absence of oxygen provides natural (?)‐isoschizogamine. Conducting the reaction in the presence of oxygen leads to a multistep oxidative hydrolysis cascade that affords unnatural (?)‐2‐hydroxyisoschizogamine.  相似文献   

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