Formal total synthesis of aspergillide A

The formal total synthesis of aspergillide A 1 is described. The cross-metathesis of enone 6 with 6-hepten-2-ol derivative 5 provided E-olefin 15 corresponding to the C₄-C₁₄ backbone of 1. The CBS asymmetric reduction of 15 gave allyl alcohol 16, which was transformed into β-alkoxyacrylate 4 which had a formyl group. SmI₂-induced reductive cyclization of 4 gave a 2,6-syn-2,3-trans THP derivative 3 in good yield. After methoxymethylation of 3, the resulting compound 19 was submitted to desilylation and hydrolysis, to afford Fuwa’s key intermediate 2 for the total synthesis of 1.     

Total synthesis of (+)-ambruticin S

A convergent total synthesis of the novel antifungal agent ambruticin S (1) has been completed from the assembly of intermediates 18, 33 and 52 that served as the respective A-, B-, and C-ring precursors. The first generation approach to a potential A-ring intermediate eventuated in the synthesis of 9a via a route that featured oxidation of the dihydroxy furan 2 and elaboration of the dihydropyranone 3 derived therefrom. Although 9a served as a precursor of 31E to complete a formal synthesis of 1, there were several inefficiencies associated with the preparation of 9a. A more expedient and efficient route to an A-ring subunit was devised that commenced with the carbohydrate-derived bisacetonide aldehyde 10 and produced 18 in five steps and 46% overall yield. The synthesis of the cyclopropyl sulfone 33 was initiated with the enantioselective cyclopropanation of 19 catalyzed by Rh₂[5(S)-MEPY]₄. Ring opening of the resultant lactone 20 followed by a series of refunctionalizations gave 33 in a total of seven steps and 46% yield from 19. Coupling of the A- and B-ring precursors 18 and 33 was then achieved via a modified Julia coupling followed by deprotection and oxidation to furnish the key intermediate 35. The dihydropyran core of the C-ring subunit precursor 49 was formed from the ring closing metathesis of the diene 48, which was prepared in three steps from the known epoxide 45, followed by oxidation. A chelation-controlled addition to the methyl ketone 49 set the stage for a stereoselective [2,3]-Wittig rearrangement that delivered the alcohol 51 that was then transformed in two steps to the sulfone 52. A traditional Julia coupling of 52 and 35 proceeded with excellent stereoselectivity, and subsequent removal of the various protecting groups gave ambruticin S (1). The longest linear sequence was 13 steps and proceeded in 4.3% overall yield.     

Total synthesis of seco-lateriflorone

A convergent strategy toward the synthesis of lateriflorone (5) is described. Our approach is based on biosynthetic considerations and draws on a sequence of prenylation, oxygenation and Claisen reactions for the construction of chromenequinone 6, and a tandem Claisen/Diels-Alder reaction cascade for the synthesis of caged tricycle 7. Union of fragments 6 and 7 led to the synthesis of seco-lateriflorone (49).     

Tandem annulation strategy for the convergent synthesis of benzonaphthopyranones: total synthesis of chartarin and O-methylhayumicinone

A Hauser-initiated tandem annulation has been developed for the rapid regiospecific synthesis of benzonaphthopyranones via formation of two rings in one-pot operation. This strategy has been generalized with benzonaphthopyranones 26, 29, 32, and 35. It has also been employed in a short synthesis of chartarin (3) and O-methylhayumicinone (67).     

Two-directional total synthesis of efomycine M and formal total synthesis of elaiolide

The anti-inflammatory agent efomycine M (1) has been synthesized from macrodilactone 38 and vinyliodide 42 by a two-directional total synthesis in 17 steps over the longest linear sequence with an overall yield of 7%. The C₂-symmetric macrodiolide 38 has been prepared by Yamaguchi macrolactonization of seco-acid 26. The central stereopentad of 1 was obtained by a highly efficient anti-aldol reaction followed by a diastereoselective ketone reduction. Additionally, we have completed a formal total synthesis of elaiolide (3) by converting macrodiolide 37 into Paterson's methylketone 13.     

The synthesis of bromo and iodo trifunctionalised tribenzosilatranes

In this report we present a direct synthesis of bromo 8 and iodo 9 trisubstituted tribenzosilatranes. Commercially available o-anisidine 1 was transformed into the triarylamine 3 in a two-step sequence, which was halogenated to furnish the tribromo 4 or the triiodo 5 substituted triamines, respectively. Subsequent deprotection of the methyl ethers furnished the novel tripod ligands 6 and 7. A transilylation reaction in the last step led to the synthesis of the desired para-halogenated tribenzosilatranes 8 and 9.     

An efficient substituent dependent synthesis of congested pyridines and pyrimidines

An efficient and versatile synthesis of various congested pyridines 3a-h, 6a,b, 8a-n, 10a-g, and 16a,b, and (pyrimidin-4-yl)acetonitriles 13a-g has been delineated by base catalyzed ring transformation of suitably functionalized 2H-pyran-2-ones 1a-h, 5, 7, and 15 by formamidine acetate 2a, acetamidine hydrochloride 2b, S-methylisothiourea 9a, pyrazol-1-yl-carboxamidine 9b, and arylamidine hydrochloride 12 separately in the presence of powdered KOH in dry DMF.     

Efficient synthesis of cephalotaxine- and deoxyharringtonine analogues by a trimethylaluminium-mediated domino reaction

The synthesis of cephalotaxine- and cephalotaxine amide analogues 14a-c and 16a-c as well as of the deoxyharringtonine analogues 5a,b was performed employing a trimethylaluminium-mediated domino reaction of 9a-c and 8 to give the spirocyclic compounds 7a-c, which was followed by a palladium catalyzed α-arylation.     

Approaches to the synthesis of arisugacin A

Approaches to the synthesis of the important acetylcholinesterase inhibitor, arisugacin A, are described. Two different routes to the key AB ring system are described: the first utilizes an intramolecular Diels-Alder reaction on a furan substrate and the second a 6π-electrocyclization of a substituted triene followed by cycloaddition with singlet oxygen. The successful synthesis of a fully functionalized AB ring system of arisugacin A, the tetraol 52 from hydroxy-β-ionone 22 in 16 steps and 9.3% overall yield is described. Several useful synthetic transformations to this molecule and its analogues are reported, e.g., the formation of the furan Diels-Alder cycloadduct 14 and its conversion into the oxa-bridged structures 17 and 21, the preparation of the dienes 25 and 26 and the conversion of the later into the endoperoxide 30 and its diol 36, the preparation of the endoperoxide 40 and the oxa-bridged system 42, and finally the use of the enelactone 43 and its ultimately successful conversion into 52. In addition, several novel rearrangements are described, producing the unusual compounds 62, 65, and 67. Finally, the successful coupling of the pyrone unit to the AB ring system is described to give compounds 70 and 71. The novel reduction of these compounds to the cyclic ether 74 is described.     

Convergent synthesis of the IJKLM-ring part of ciguatoxin CTX3C

Convergent synthesis of the IJKLM-ring part (2) of ciguatoxin CTX3C has been achieved from the I-ring and the L-ring parts (4 and 5) in total eight steps in 27% overall yield. The carbanion derived from 4, stabilized by a dimethyldithioacetal S-oxide group, was readily reacted with aldehyde 5 to give an adduct, which was facilely transformed into the corresponding α,ε-dihydroxy ketone 3. The JK-ring formation from 3 under reductive conditions followed by oxidative M-ring cyclization efficiently led to the pentacyclic ether 2. Improved synthesis of 6, a synthetic intermediate for 4, was also established.     

The second generation synthesis of (+)-pseudodeflectusin

The second generation synthesis of (+)-pseudodeflectusin (1), a potential antitumor agent, has been achieved. The key synthetic step is the cascade reaction involving Diels-Alder reaction, lactonization, and decarboxylation to give cycloadduct 6 with complete regioselectivity in good yield. We found that NaH is the best base to facilitate the Diels-Alder reaction of hydroxypyrone 7 with alkyne 8. The present synthetic route enables the total synthesis of (+)-1 in only five-steps from the known compounds 7 and 8.     

A Wacker-Cook synthesis of isoflavones: formononetine

A total synthesis of the isoflavone formononetine 1 by an oxidative Pd-mediated cyclization of α-methylenedeoxybenzoins 4a-c is described. Substrates 4a-c were rapidly assembled using ‘protected cyanohydrin’ chemistry.     

Simple and efficient synthesis of highly functionalized cyclohexanes; formal total synthesis of ovalicin and fumagillin

Two chiral cyclohexanes 4 and 6, which are key intermediates for the total synthesis of ovalicin 1 and fumagillin 2, respectively, were synthesized from (2R,3S) 1,2-epoxy-4-penten-3-ol. The key steps involve an efficient construction of divinylalcohol 7 using methallyl Grignard reagent 9c, and an intramolecular olefin metathesis of 7.     

Quinoxaline-annelated Z-shaped quadruple-bridged orthocyclophanes: synthesis and crystal structures

A three-step synthesis of nineteen Z-shaped quadruple-bridged [6,6] and [6,4]orthocyclophanes comprising two quinoxaline-based sidewalls are described. The synthesis began from the bis-Diels−Alder adducts B1-B3 followed by ruthenium-promoted oxidation of dichloroetheno-bridges in the adducts to generate a bis-α-diketones, which were then condensed with various arene-1,2-diamines (9a-g) to construct sidewalls (phane parts) of Z-shaped quadruple-bridged orthocyclophanes D1-3, D2g, and D3g. Single-crystal structures of six orthocyclophanes (D1a, D2a, D2f, D3f, D2g-α, and D3g-α) were obtained and revealed that the C_Ar−H?π and π?π stacking interactions between N-containing arene rings are the major driving force for molecular assembly and crystal packing, in addition to the interactions involving the polar OCH₃ groups and the solvate molecules.     

Amberlyst 15 catalyzed synthesis of indole-pyrazole based tri(hetero)arylmethanes

An expedient synthesis of 1,3-diaryl-4-(3,3′-diindolyl)methylpyrazoles 3a-m has been developed using Amberlyst 15 catalyzed condensation of 1,3-diaryl-4-formyl pyrazoles 2 with indoles 1. This reaction was further extended to the synthesis of 4,4′-bis(3,3′-diindolyl)methylphenoxy-alkanes 5a-b by coupling of 4,4′-di(formylphenoxy)alkane 4 with indole 1.     

A novel and practical synthetic route for the total synthesis of lycopene

A novel route for the total synthesis of lycopene 1 is described. The synthesis is based on: (i) a condensation between 4,4-dimethoxy-3-methylbutanal 4 and methylenebisphosphonic acid tetraethyl ester 5, leading to the C6-phosphonate 6, followed by (ii) a modified Wittig-Horner reaction between 6 and 6-methyl-5-hepten-2-one 7 producing dimethoxy-3,5,9-triene 8, and (iii) another modified Wittig-Horner reaction between C15-phosphonate 2 and C10-triene dialdehyde 3 producing all-E-lycopene. The synthetic steps are easily operated and practical for the large-scale production.     

Regioselective synthesis of 4- and 5-oxazole-phosphine oxides and -phosphonates from 2H-azirines and acyl chlorides

A simple and efficient regioselective synthesis of 4-oxazole-phosphine oxides 11 and -phosphonates 12 from 2H-azirine-phosphine oxides 1 and -phosphonates 6 is described. The key step for the synthesis of oxazoles 11 is a base-mediated ring closure of vinylogous α-aminophosphorus compounds derived from phosphine oxides 4 and from phosphonates 8. These derivatives 4 and 8 are obtained by reaction of functionalized azirines 1 and 6 with acyl chlorides 2 and subsequent acid-catalyzed ring opening of N-acylaziridine-phosphine oxides 3 and -phosphonates 7. Regioselective thermal ring cleavage of N-acylaziridine-phosphine oxides 3 leads α-chloro-β-(N-acylamido)-phosphine oxides 13 and their treatment with bases gives 5-oxazole-phosphine oxides 16.     

General entries to C-aryl glycosides. Formal synthesis of galtamycinone

Utilizing a general entry we had developed for the synthesis of C-aryl glycosides, we have prepared the juglone derivatives 18-20 as well as the juglone precursor 13. Because 19 had been previously converted in two steps by Suzuki into galtamycinone (1), its preparation constitutes a total synthesis of 1.     

Total synthesis of the mushroom metabolite (+)-calopin

A synthesis of (+)-calopin (1a) was achieved employing a highly stereoselective ene reaction between 8-phenylmenthyl glyoxylate (3) and the β,β-dimethylstyrene 4c. Transesterification of the resulting homoallylic alcohol 5c, followed by allylic oxidation and hydrogenation yielded the δ-lactone 13 which was deprotected to the natural product 1a.     

New synthesis of glycolipid immunostimulants RC-529 and CRX-524

An efficient and scalable synthesis of the potent vaccine adjuvant RC-529 (3) and TLR4 agonist CRX-524 (4) is described in eight steps from 1,3,4,6-tetra-O-acetyl-2-amino-2-benzyloxycarbonyl-2-deoxy-β-d-glucopyranose (10c) in ca. 25% overall yield. The synthesis features the strategic use of the N-Cbz group for β-glycosylation and the selective N,N,O-triacylation of common advanced intermediate 15 with (R)-3-tetradecanoyloxy or decanoyloxytetradecanoic acid (8, 9) late in the synthesis. A new method for preparing and enhancing the enantiopurity of (R)-3-hydroxytetradecanoic acid (6), a key component of 3 and 4 as well as bacterial lipid A, is also described.