Total synthesis of spatol and other spatane diterpenes
摘要:
Total syntheses of three spatane diterpenes stoechospermol (1), 5(R),15(R),18-trihydroxyspata-13,16(E)-diene (2), and (+)-spatol (3) were accomplished from a common intermediate, diol 7. The total synthesis established as R the absolute configuration at the 15-position in 2. Novel stereospecific transformations of 2,3-epoxy-1,4-diols into vicinal diepoxides were demonstrated and exploited for assembling the sensitive allylic diepoxide in the side chain of spatol. This new synthetic method allows the conversion of both 1,2-threo-2,3-trans- and 1,2-erythro-2,3-trans-2,3-epoxy-1,4-diols into vicinal 1,2-cis-2,3-erythro-1,3-diepoxides. Unexpected stability toward hydroxide anion was found for the allylic diepoxide functional array. This observation provides presumptive evidence that acid catalysis is operative in the epoxide cleaving substitution reaction of spatol by the weakly nucleophilic chloride anion that gives chlorohydrin 4. A proclivity for erythro-selective epoxidation of allylic silyl ethers was found. The utility of C-silyl substituents for reversing this stereoselectivity, i.e., favoring threo-selective epoxidation of allylic silyl ethers, was established.
The methyl malonate esters of 3-buten-1-ol and 2-methyl-3-buten-1-ol can be coupled efficiently to different methallylic esters in the presence of the second-generation Grubbs catalyst to yield trisubstituted olefins by the cross-metathesis reaction. Product selectivity and yields depend on the relative amounts of reagents and to a minor extent on the methallylic ester functional group. Alkyl substituents
Here we report the development of a straightforward synthetic procedure for the preparation of spirocyclic endoperoxides as synthetic analogues of the natural product dihydroplakortin. The peroxides presented here are more potent antiplasmodials than dihydroplakortin itself and we proved for the first time their antimalarial activity in vivo.
Ruthenium-Catalyzed Alkene–Alkyne Coupling of Disubstituted Olefins: Application to the Stereoselective Synthesis of Trisubstituted Enecarbamates
作者:Barry M. Trost、James J. Cregg
DOI:10.1021/ja511911b
日期:2015.1.21
The Ru-catalyzed alkene-alkynecoupling reaction has been demonstrated to be an enabling methodology for the synthesis of complex molecules. However, to date, it has been limited to monosubstituted olefins. Herein we report the first general utilization of disubstituted olefins in the Ru-catalyzed alkene-alkynecoupling reaction by employing carbamate directing groups. The products are stereodefined
作者:Yi An Cheng、Wesley Zongrong Yu、Ying-Yeung Yeung
DOI:10.1002/anie.201504724
日期:2015.10.5
A highly facile, efficient, and enantioselectivebromolactamization of olefinic amides was effected by a carbamate catalyst and ethanol additive. The amide substrates underwent N‐cyclization predominantly to give a diverse range of enantioenriched bromolactam products containing up to two stereogenic centers.
Rhodium-Catalyzed Asymmetric Hydroformylation of 1,1-Disubstituted Allylphthalimides: A Catalytic Route to β<sup>3</sup>-Amino Acids
作者:Xin Zheng、Bonan Cao、Tang-lin Liu、Xumu Zhang
DOI:10.1002/adsc.201200960
日期:2013.3.11
enantioselective rhodium‐catalyzed hydroformylation of 1,1‐disubstituted allylphthalimides has been developed. By employing chiral ligand 1,2‐bis[(2S,5S)‐2,5‐diphenylphospholano]ethane [(S,S)‐Ph‐BPE], a series of β3‐aminoaldehydes can be prepared with up to 95% enantioselectivity. This asymmetric procedure provides an efficient alternative route to prepare chiral β3‐amino acids and alcohols.