Fluoride-mediated elimination of allyl sulfones: application to the synthesis of a 2,4-dimethyl-A-ring vitamin D3 analogue

A coupling strategy for the synthesis of 2,4-dimethyl-1α,25(OH)(2)D(3) is achieved which involves methylation of a pro-A ring vinyl sulfone and in situ traping of the allyl sulfonyl anion with a CD ring allyl chloride. TBAF-promoted 1,2-eliminative desulfonylation and concomitant silyl ether deprotection gives the vitamin D(3) analogue.     

An enantioselective synthesis of the A-ring synthon for vitamin D3 metabolites by chemicoenzymatic approach

The A-ring synthon for vitamin D3 metabolites having 1α hydroxyl group is synthesized starting from a chiral monoester 6 enzymatically generated.     

Organosilanes in synthesis: application to an enantioselective synthesis of methyl-l-callipeltose

[reaction: see text] Methyl-l-callipeltose, the carbohydrate associated with callipeltoside A, has been synthesized in eight steps and 23% overall yield from enantioenriched allylsilane 6 and acetaldehyde. The key steps are a highly diastereoselective formal [4 + 2] annulation and a Cr(VI)-catalyzed oxidative C-C bond cleavage to produce lactone 11.     

Catalytic enantioselective synthesis of naturally occurring butenolides via hetero-allylic alkylation and ring closing metathesis

An efficient catalytic asymmetric synthesis of chiral γ-butenolides was developed based on the hetero-allylic asymmetric alkylation (h-AAA) in combination with ring closing metathesis (RCM). The synthetic potential of the h-AAA-RCM protocol was illustrated with the facile synthesis of (-)-whiskey lactone, (-)-cognac lactone, (-)-nephrosteranic acid, and (-)-roccellaric acid.     

A highly enantioselective one-pot synthesis of homoallylic alcohols via tandem asymmetric allyl transfer/olefin cross metathesis

A highly enantioselective one-pot synthesis of linear homoallylic alcohols with terminal ester functionality has been achieved. The reactions were controlled by ordered addition of reagents and catalysts, ensuring complete consumption of aldehyde. The synthetic utility of this strategy has been demonstrated in a short synthesis of a low boiling point intermediate for grahamimycin A.     

A novel enantioselective alkylation and its application to the synthesis of an anticancer agent

A novel enantioselective alkylation of double benzylic substrates with secondary electrophiles is reported. A simple norephedrine-based chiral ligand was synthesized that gives alkylation product in 95% yield and 95% ee. A unique water effect on the enantioselectivity was unveiled. Good to excellent ee values were obtained with a number of double benzylic substrates and secondary electrophiles. This novel reaction has been applied to the synthesis of a promising anticancer agent.     

Syntheses of 3-substituted furans via lithium di(3-furyl)cuprate—the application of lithium di(3-furyl)cuprate to the total synthesis of dendrolasin

One step syntheses of 3-substituted furans by the reactions of a new reagent, lithium di(3-furyl)cuprate $\text{1}$, with various substrates and the application of $\text{1}$ to a total synthesis of dendrolasin are described.     

A synthesis of vitamin A according to the sulfone method (author's transl)]

A Synthesis of Vitamin A According to the Sulfone Method. Starting from β-ionyl phenyl sulfone 7 and an appropriate allylic chloride 10 retinol 14 has been prepared by a direct procedure. Subsequent acetylation and isomerization led to crystalline all-E-vitamin A acetate 16 .     

Olefination of ketenes for the enantioselective synthesis of allenes via an ylide route

Pseudo-C₂-symmetric chiral phosphorus ylide is designed and synthesized for the enantioselective preparation of allenic esters, amides, ketone, and nitrile. Up to 92% ee is achieved.     

Tandem cross-metathesis/hydrogenation: application to an enantioselective synthesis of pentadecyl 6-hydroxydodecanoate

The synthesis of pentadecyl 6-hydroxydodecanoate, a component isolated from the leaves of Artabotrys odoratissimus, has been achieved through a tandem cross-metathesis/hydrogenation sequence. The enantioselective synthesis required first the preparation of a homoallylic alcohol obtained by a free-metal allyl transfer from a camphor derivative to heptanal.     

A new approach to fused furan ring systems and benzofurans: Intramolecular cyclization reactions of unsaturated acyloxy sulfone derivatives

Unsaturated acyloxy sulfones 3 undergo intramolecular cyclization upon deprotonation with LHMDS in THF. Dehydration and double bond isomerization of the products upon exposure to acid, gave the fused ring furans, 4, in good yields. This strategy could be readily adapted to prepare substituted benzofurans 12 from the cyclization reactions of acyloxy sulfones 11 prepared from phenols. Finally, this approach could be successfully modified to access dihydropyrans and benzopyrans.     

Polysubstituted piperidines via iodolactonization: application to the asymmetric synthesis of (+)-pseudodistomin D

Conjugate addition of lithium (S)-N-allyl-N-(α-methyl-p-methoxybenzyl)amide to methyl (E,E)-hepta-2,5-dienoate furnished the corresponding β-amino ester. N-Protecting group manipulation, ring-closing metathesis, and ester hydrolysis gave enantiopure [N(1')-tert-butoxycarbonyl-1,2,3,6-tetrahydropyridin-2'-yl]ethanoic acid. Subsequent iodolactonization gave a bicyclic iodolactone scaffold. This key intermediate was elaborated to (+)-pseudodistomin D [in >99% ee and 7% yield over 16 steps from methyl (E,E)-hepta-2,5-dienoate].     

An approach to an enantioselective synthesis of crisamicin A via a novel double Hauser-Kraus annulation strategy

A double Hauser-Kraus annulation between biscyanophthalide 4 and the d-mannose derived enone 39 provides access to an advanced intermediate 54 that is an excellent scaffold to effect an enantioselective total synthesis of crisamicin A 1.     

Asymmetric total synthesis of sperabillins B and D via lithium amide conjugate addition

Diastereoselective conjugate addition of homochiral lithium (R)-N-allyl-N-alpha-methylbenzylamide to methyl (2E,5E)-hepatadienoate, followed by protecting group manipulation and subsequent iodocyclocarbamation allows a concise route to the core fragment, methyl (3R,5R,6R)-3,6-diamino-5-hydroxyheptanoate, of sperabillins B and D. Differentiation between the C-3 and C-6 primary amino groups of this core amino acid was readily achieved by treatment with acetone, giving the 5,6-isopropylidene and C-3-imine protected diamine, with subsequent regioselective acylation of the C-6-nitrogen facilitating the total synthesis of sperabillin D in 10.8% overall yield, and the first asymmetric synthesis of sperabillin B in 5.8% overall yield.     

A simplified catalytic system for direct catalytic asymmetric aldol reaction of thioamides; application to an enantioselective synthesis of atorvastatin

A new catalytic system was developed for the direct catalytic asymmetric aldol reaction of thioamides. The new lithium-free Cu catalyst (second-generation catalyst) exhibited enhanced catalytic efficiency over the previously developed catalyst comprising [Cu(CH₃CN)₄]PF₆/Ph-BPE/LiOAr (first-generation catalyst), which required a tedious catalyst preparation process. In the reaction with the second-generation catalyst, the intermediate Cu-aldolate functioned as a Brønsted base to generate thioamide enolate, efficiently driving the catalytic cycle. The present aldol methodology culminated in a concise asymmetric synthesis of atorvastatin (Lipitor^®: atorvastatin calcium), a widely prescribed HMG-CoA reductase inhibitor for lowering low-density lipoprotein cholesterol.     

The first example of enantioselective allyl transfer from a linear homoallylic alcohol to an aldehyde

[reaction: see text] The first example of enantioselective linear homoallylic alcohol transfer reaction was revealed. In all cases, the whole rearrangement is thermodynamically favorable and a steric effect is the driving force of this reaction. The preservation of the stereocenter and olefin geometry together with the isolation of gamma-adduct homoallylic alcohols in one isomeric form have warranted the proposed mechanism.     

Intramolecular diels-alder reactions of benzynes application to the total synthesis of mansonone E

Substituted benzynes san be trapped intramolecularly by an attached furan moiety and such a reaction has been used in the synthesis of the naturally occurring o-naphthoquin- one mansonone E.     

Asymmetric synthesis of unsaturated α-benzyloxyaldehydes: an enantioselective synthesis of (+)-exo-brevicomin

Enantioselective synthesis of α-hydroxy aldehydes with an alkene tether was accomplished from l-(+)-tartaric acid, employing stereoselective reduction of a 1,4-diketone with L-selectride as the key step. Synthetic utility of these aldehydes was demonstrated in the synthesis of pine beetle pheromone (+)-exo-brevicomin.