An enantioselective synthesis of (S)- and (R)-curcuphenol

The enantioselective synthesis of the phenolic sesquiterenses (S)- and (R)-curcuphenol is reported. The key step in this synthesis is the asymmetric conjugate addition using a readily available enantiomerically pure sulfoxide as the chiral auxiliary.     

Total Synthesis of (+)-(8S,13R)-Cyclocelabenzine

An asymmetric synthesis of the spermidine alkaloid (+)-cyclocelabenzine ( 1a ) and its (?)-(13S)-epimer 1b is described using optically active (+)-(3S)-3-amino-3-phenylpropionic acid as the chiral building block. The isoquinolin-1-one fragment 15 was synthesized by a modified Bischler-Napieralski reaction. The relative configuration of the (?)-isomer was determined by an X-ray crystal-structure analysis, which enabled us to determine the absolute configuration of natural (+)- 1a as (8S,13R).     

Novel sparteine-mediated enantio-dichotomic formal synthesis of R-(-)- and S-(+)-curcuphenol

High and opposite enantiodiscriminations were observed between tertiary amides and secondary amides in the sparteine-mediated lateral metalation-allylation of 2-ethyl-m-toluamide derivatives (2a, 2e). The results described above have been applied for the formal synthesis of both enantiomers of curcuphenol. The brief mechanistic studies suggested that stereoinformation was introduced after the deprotonation step.     

(+)-(1S,2S,5R)-8-联苯薄荷醇的合成

以(R)-( )-pu legone为起始原料,经1,4-加成,还原两步反应合成了手性辅助试剂( )-(1S,2S,5R)-8-联苯薄荷醇及其差向异构体(-)-(1R,2S,5R)-8-联苯薄荷醇,总产率95%。其结构经1H NMR,13C NMR,IR,MS和X-射线衍射仪表征。     

Total synthesis of (-)-barbatusol, (+)-demethylsalvicanol, (-)-brussonol, and (+)-grandione

The icetexane-based diterpenes (-)-barbatusol, (+)-demethylsalvicanol, and (-)-brussonol were synthesized. Synthetic demethylsalvicanol was dimerized to produce (+)-grandione using aqueous Diels-Alder conditions.     

Total synthesis of (S)-(+)-ent-phomapyrones B and surugapyrone B

Phomapyrone B ( 1 ), the 2-pyrones isolated from the phytopathogenic fungus Leptosphaeria maculans, has been synthesized as the enantiomeric form starting from (S)-2-methylbutanol ( 4 ). Surugapyrone B ( 3 ) isolated from Streptmyces sp. USF-6280 as an antioxidant has also been synthesized as a natural form. The absolute configuration of phomapyrone B ( 1 ) was estimated to be the (R)-form and that of surugapyrone B ( 3 ) being the (S)-form. A series of 2-pyrone derivatives 17 have been synthesized through the established procedure and their DPPH radical-scavenging activities have also been evaluated.     

Total synthesis of (-)- and (+)-dysibetaine

Glycidamides 6R and 6S were elaborated to (R,R)- and (S,S)-dysibetaines (1R and 1S) by intramolecular alkylation and functional group modification in 23% overall yield. The absolute stereochemistry of natural dysibetaine was established as S,S by comparison of the optical rotation of the natural product with that of the synthetic materials.     

Total synthesis of (-)- and (+)-lentiginosine

Total synthesis of (-)-lentiginosine was achieved from D-mannitol using highly stereoselective reactions. Similarly, (+)-lentiginosine was synthesized from L-tartaric acid.     

Total synthesis of (3R, 4S)-4-hydroxylasiodiplodin

Abstract

An alternative and concise total synthesis of (3?R, 4S)-4-Hydroxylasiodiplodin has been reported from inexpensive and commercially available 6-heptenal and Orsellinic acid starting materials. The key steps involved in the synthesis are Wittig reaction, Sharpless epoxidation, Yamaguchi esterification and ring-closing metathesis (RCM).     

Benzothiazines in synthesis. Formal syntheses of (+)-curcumene and (+)-curcuphenol

A benzothiazine readily available in enantiomerically pure form via a stereoselective, intramolecular Michael addition reaction could be converted to a precursor to (+)-curcuphenol and to (+)-curcumene.     

Total synthesis of (R)-(+)-salsolidine by hydride addition to (R)-N-tert-butanesulfinyl ketimine

(R)-(+)-Salsolidine 1 of high enantiomeric purity was synthesized using the Pomeranz–Fritsch–Bobbitt methodology, in which the reduction (NaBH₄, DIBAL-H) of N-tert-butanesulfinyl ketimine, derived from 3,4-dimethoxyacetophenone, was the key step. The synthesis was completed in a sequence of reactions involving the removal of the chiral auxiliary, N-alkylation with 2,2-diethoxyethyl bromide and final cyclization/hydrogenolysis.     

Concise synthesis of (S,S)-(+)-dehydrohomoancepsenolide

A concise total synthesis of the bis-butenolide 3 in optically active form is reported. Key steps are a zinc-mediated "three-component coupling" with formation of dienyne 9 which undergoes ring closing metathesis (RCM) on treatment with (PCy(3))(2)Cl(2)Ru=CHPh. Dimerization of the resulting butenolide 11 is then achieved via alkyne metathesis using (tBuO)(3)W&tbd1;CCMe(3) as the catalyst. A Lindlar reduction completes this synthesis which delivers product 3 in only five steps with an overall yield of 25%.     

A general enantioselective approach to jasmonoid fragrances: synthesis of (+)-(1R,2S)-methyl dihydrojasmonate and (+)-(1R,2S)-magnolione

Methyl dihydrojasmonate 1 and magnolione 3 are of both academic and industrial interest. In this paper, we describe a flexible, high-yielding route to diastereomerically pure (+)-cis-(1R,2S)-methyl dihydrojasmonate 1 and the first synthesis of (+)-cis-(1R,2S)-magnolione 3, both with enantiomeric excesses up to 93%. The two syntheses diverged from the same advanced intermediate 5, readily available from the enantioenriched hydroxymethyl delta-lactone (-)-(3aS,4S,6aR)-6. The olfactory properties of (1R,2S)-1 and (1R,2S)-3 are reported.     

Total synthesis of (-)- and (+)-membrenone C

[reaction: see text] A synthesis of the polypropionate marine defense substance (+)-membrenone C and its enantiomer that starts from (S)-2-methyl-3-(tert-butyldimethylsilyloxy)propanal is described. Key steps include (1) additions of chiral allenylmetal reagents to effect both chain homologation and the concomitant introduction of four stereo centers, (2) a bis-intramolecular hydrosilylation-oxidation sequence to install beta-hydroxy ketone subunits, and (3) a bis-intramolecular aldol reaction to construct the two dihydropyrone termini.     

Total synthesis of (-)- and ent-(+)-vindoline

[reaction: see text] Two exceptionally concise total syntheses of (-)- and ent-(+)-vindoline are detailed enlisting a diastereoselective tandem [4 + 2]/[3 + 2] cycloaddition of a 1,3,4-oxadiazole. The unique reaction cascade assembles the fully functionalized pentacyclic ring system of vindoline in a single step that forms four C-C bonds and three rings while introducing all requisite functionality and setting all six stereocenters within the central ring including three contiguous and four total quaternary centers.     

Total synthesis of (-)-incarvilline, (+)-incarvine C, and (-)-incarvillateine

The first total syntheses of new monoterpene alkaloids (-)-incarvilline, (+)-incarvine C, and (-)-incarvillateine, corresponding to the natural enantiomers, have been accomplished. The strategy for the synthesis of these natural products utilized 6-epi-incarvilline as a common precursor, which was assembled by a three-component coupling reaction using (4S)-4-siloxy-2-cyclopenten-1-one to construct an appropriately trisubstituted cyclopentanone, followed by ring closure to the cis-perhydro-2-pyrindine skeleton by means of a reductive Heck-type reaction. Furthermore, topochemically controlled [2 + 2] photodimerization of cinnamic acid derivatives in the solid state for the stereospecific construction of a 1,2,3,4-tetrasubstituted cyclobutane ring was also investigated as a means to access (-)-incarvillateine.     

Total synthesis of (S)-(+)-tylophorine via enantioselective intramolecular alkene carboamination

The enantioselective synthesis of (S)-(+)-tylophorine, a potent cancer cell growth inhibitor, has been accomplished in eight steps from commercially available 3,4-dimethoxybenzyl alcohol. A copper (II)-catalyzed enantioselective intramolecular alkene carboamination was employed as the key step to construct the chiral indolizidine ring.     

Terpenes in organic synthesis. 8. Synthesis of optically active (2R/S, 3S, 7R/S)-(-)-diprionyl acetate from (S)-(+)-3,7-dimethyl-1,6-octadiene

Conclusions A seven-stage synthesis has given optically active (2R/S, 3S, 7R/S)-2-acetoxy-3,7-dimethylpentadecane from the readily available (S)-(+)-3,7-dimethyl-1,6-octadiene, in an overall yield of 36%. The synthetic route utilizes all ten carbon atoms of the starting chiral diene.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1142–1146, May, 1988.