Efficient formal synthesis of (±)-axamide-1 and (±)-axisonitrile-1 via an intramolecular Hosomi-Sakurai reaction

A formal synthesis of (±)-axamide-1 and (±)-axisonitrile-1 was achieved by using an intramolecular Hosomi-Sakurai reaction of the allylsilane derivative, as a key step, in which [(3-but-3-en-1-yl-3-methylcyclohex-1-en-1-yl)methyl](trimethyl)silane was transformed to a bicyclic compound possessing a core carbon framework under the oxidative dihydroxylation reaction conditions, in one step.     

Synthesis of (±)-kuwanon V and (±)-dorsterone methyl ethers via Diels-Alder reaction

The mulberry Diels-Alder adducts, the pentamethyl ethers of kuwanon V 1a and dorsterone 2a were synthesised via a biomimetic intermolecular [4+2] cycloaddition reaction between a highly electron-rich dienophile and a Lewis acid sensitive diene derived from chalcone. Cycloaddition under thermal conditions afforded 1a and 2a (in 3:2 ratio). Cycloaddition catalysed by AgOTf/Bu₄NBH₄ gave higher yields of the adducts.     

Synthesis of (±)-cartorimine

Heating pyranulose 4 and cinnamate 2 in the presence of 2,6-di-t-butylpyridine in CH₃CN afforded the [5+2] cycloadduct, which was hydrolyzed to give 13% of cartorimine (1).     

Synthesis of bicyclo[2.2.2]oct-5-en-2-ones via a tandem intermolecular Michael addition intramolecular aldol process (a bridged Robinson annulation)

A novel one-pot synthesis of the several bicyclo[2.2.2]oct-5-en-2-ones 19 has been developed in which a cyclic or acyclic ketone 18 is reacted with a cyclic enone 6 in the presence of strong acid to give the bicyclic enone product 19. Alternatively, the intermediate diketone 21 can be prepared separately and subjected to the reaction conditions to give the bicyclic enones 19 in good yields.     

Synthesis of (±)-aporphine utilizing Pictet-Spengler and intramolecular phenol ortho-arylation reactions

A synthesis of the alkaloid (±)-aporphine is reported. The initial key step of the synthesis involves a Pictet-Spengler cyclization of N-tosyl tyramine with 2-bromophenylacetaldehyde in trifluoroacetic acid. This step was followed by the second strategic transformation a palladium-mediated intramolecular phenol ortho-arylation reaction utilizing tricyclohexylphosphine as co-catalysts in the presence of cesium carbonate. Finally, de-oxygenation of the phenol, removal of the tosyl group and methylation gave the desired alkaloid.     

Synthesis of (±)-coerulescine and a formal synthesis of (±)-horsfiline

A straightforward synthesis of (±)-coerulescine and (±)-horsfiline has been established from 3-formyl-3-phenylpyrrolidine employing 4-hydroxypiperidine as the starting material. There are two remarkable steps for the synthesis of (±)-coerulescine and (±)-horsfiline. One is the rapid access to produce 3-formyl-3-phenylpyrrolidine by Lewis acid-catalyzed rearrangement of 3,4-dihydroxy-4-phenylpiperidine. The other key step is an intramolecular electrophilic cyclization from 3-benzylcarbamoyl-3-phenylpyrrolidine to the 3,3-spirocyclic 2-oxindole ring skeleton.     

天然产物(±)-Lupinine和(±)-Epilupinine的简便合成

羽扇豆碱和表羽扇豆碱是典型的喹诺里西啶类生物碱。以哌啶酸乙酯盐酸盐为原料,通过氮烷基化反应、迪克曼缩合反应、Krapcho脱羰反应、Wittig反应等4步反应制得关键中间体5,总产率46.7%。化合物5可经文献转化,完成(±)-lupinine和(±)-epilupinine的合成。该合成方法具有合成路线短,产率高以及操作简单等优点。      

(±)-Mesembrine的全合成

以3-乙氧基-2-环己烯酮羰基邻位芳基化反应与Tsuji-Trost反应的串联反应作为关键步骤来构筑季碳中心, 完成了番杏科生物碱Mesembrine的全合成. 从商品化原料出发经6步反应以17.8%的总收率合成得到(±)-Mesembrine.     

Novel total syntheses of (±)-oxerine by intramolecular Heck reaction

Both a three-step and a five-step syntheses of monoterpene alkaloid (±)-oxerine from alcohol 6 have been accomplished. In the second approach, the synthetic efficiency was enhanced by implementing a one-pot protocol (deprotonation/silylation/ alkylation/desilylation). The construction of the cyclopenta[c]pyridine framework was realized by an intramolecular Heck reaction, which should be adaptable for the synthesis of other related monoterpene pyridine alkaloids.     

Synthesis of BN-fused polycyclic aromatics via tandem intramolecular electrophilic arene borylation

A tandem intramolecular electrophilic arene borylation reaction has been developed for the synthesis of BN-fused polycyclic aromatic compounds such as 4b-aza-12b-boradibenzo[g,p]chrysene (A) and 8b,11b-diaza-19b,22b-diborahexabenzo[a,c,fg,j,l,op]tetracene. These compounds adopt a twisted conformation, which results in a tight and offset face-to-face stacking array in the solid state. Time-resolved microwave conductivity measurements prove that the intrinsic hole mobility of A is comparable to that of rubrene, one of the most commonly used organic semiconductors, indicating that BN-substituted PAHs are potential candidates for organic electronic materials.     

Access to resorcylic acid lactones via phosphonate based intramolecular olefination

An approach to resorcylic acid lactones is described, exploiting an intramolecular olefination reaction for the generation of the 14-membered macrolactone. The synthetic route gave zearalenone precursors, and the preparations of other RAL analogues, trans- and cis-resorcylides are included, the latter being prepared by photoisomerization of the trans-isomer. β-Haloketone derivatives were also prepared in a highly stereoselective manner by conjugate addition of chloride or bromide to the E-enone using boron trichloride and boron tribromide, respectively.     

Synthesis of bridged azabicycles from isoquinolines via a tandem of allylboration and intramolecular metathesis

A method for the synthesis of bridged azabicyclic compounds from isoquinolines was developed. The method is based on a combination of allylboration and ruthenium-catalyzed intramolecular metathesis. Reductive 1,3-diallylation of bromoisoquinolines with triallylborane gave trans-1,3-diallyl-1,2,3,4-tetrahydroisoquinolines. When heated with triallylborane, these compounds yielded mixtures of cis-and trans-isomers in the ratio ∼1: 1. The structure of cis-1,3-diallyl-5-bromo-1,2,3,4-tetrahydroisoquinoline was confirmed by X-ray diffraction analysis. In a similar way, trans-3-allyl-1-vinyl-1,2,3,4-tetrahydroisoquinoline synthesized by sequential vinylation (with vinyllithium) and allylboration of isoquinoline, yielded a mixture of cis-and trans-isomers in the ratio 1.6: 1. Intramolecular metathesis reactions of N-Boc derivatives of cis-isomers in the presence of the Grubbs catalyst (2.0–2.5 mol.%) afforded 7,8-benzo-10-azabicyclo[4.3.1]dec-2-enes or 7,8-benzo-9-azabicyclo[3.3.1]non-2-ene in nearly quantitative yields. Dedicated to Academician V. A. Tartakovsky on the occasion of his 75th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1510–1515, August, 2007.     

A short synthesis of (±)-tecomanine via a Pauson-Khand-based route

The N-carboethoxy precursor to (±)-tecomanine has been prepared in 11 steps from 2-methyl-1-buten-3-yne. The key step, Pauson-Khand cyclization of a methylated 5-aza-6-nonen-1-yne succeeds, but only in low yield, a consequence of the dialkyl substitution about the azaenyne framework. Nevertheless, the overall sequence to that point is one of the more efficient to be described.     

(±)-脱落酸的合成

以β-紫罗兰酮为起始原料,经环氧化、开环、烯丙位氧化、Wittig反应、碱性水解5步反应,以39％的总收率合成了植物激素3-甲基-5-(1-羟基-4-氧代-2,6,6-三甲基-2-环己烯基)-2,4-戊二烯酸(脱落酸),用IR、¹H NMR、MS及元素分析等测试技术表征了产物的结构。     

天然产物(±)-Aiphanol的全合成研究

以醛1和5为起始原料,经几步反应后用Ag₂O偶联,得到含苯并二氧六环骨架的化合物7,化合物7经过选择性保护酚羟基,再用NaIO₄/OsO₄(cat.)氧化断裂双键,得到关键中间体9,化合物9和10经过Wittig-Horner反应,并用苯硫酚和AIBN实现了顺式双键向反式的转化,脱去保护基后完成了具有新颖结构的天然产物(±)-Aiphanol(12)的合成.     

Total synthesis of (-)-kainic acid via intramolecular Michael addition: a second-generation route

A total synthesis of (-)-kainic acid starting from the commercially available 2-azetidinone is described. The key delta-lactone intermediate was concisely prepared from the commercially available azetidinone through the Reformatsky-type reaction and an introduction of a glycine moiety. The construction of the functionalized pyrrolidine ring was executed by a one-pot sequential elimination-Michael addition protocol of a beta-amino-delta-lactone intermediate with high diastereoselectivity.     

A Novel Approach towards 2,3,5-Trisubstituted Thiophenes via tandem Michael addition/intramolecular Knoevenagel condensation

Starting from the easily available, highly functionalized acetylenic ketories 4a–i (Scheme 1), novel 2,3,5-trisubstituted thiophenes 1a–i (Scheme 2) were synthesized in good yields using a tandem Michael-addition/intramolecular Knoevenagel-condensation strategy, featuring Cs₂CO₃/MgSO₄ (1:2) as an efficient base to effect the cyclization. Subsequent simple one-step transformations yielded 2,3-disubstituted thiophene-5-carbaidehydes 7a–c , carboxylic-acid derivatives 8, 9 , and 11 , and alcohol 10 (Scheme 3). These molecules constitute interesting novel thiophene-containing building blocks, useful for the preparation of low-molecular-weight compound libraries by combinatorial and parallel-chemistry techniques.     

Synthesis of (±)-solanapyrones A and B

In this paper we report the development of a stereoselective IMDA approach to the phytotoxic polyketides (±)-solanapyrones A and B. The stereoselectivity of the key IMDA cycloaddition was optimized by investigating a range of 2,8,10-dodecatrienoic acid derivatives. This established that use of the Weinreb amide led to the desired exo-selectivity and also facilitated construction of the pyrone moiety. A novel approach to the installation of the C-3 formyl group in solanapyrone A is also described.     

Synthesis of the necine bases (±)-macronecine and (±)-supinidine via an aza-ene reaction and allylsilane induced ring closure

An aza-ene reaction has been used for the first time for the synthesis of two 5-membered lactam-hydrazides, each with a built-in allylsilane terminator for further elaboration. One of the lactam-hydrazides was transformed via an allylsilane-hydrazonium ion ring closure to a fused tetrahydropyrazole which may be considered as a mono-nitrogen analog of the biologically significant necine bases. A density functional theoretical study (B3LYP/6-21G*) was undertaken to provide insight into the factors that favor a synclinal transition structure of the hydrazonium ion intermediate leading to the tetrahydropyrazole. This stereocontrolled synthesis served as a model for the multi-step conversion of the other lactam-hydrazide, the substituted 2-pyrrolidinone, to necine bases (±)-supinidine and (±)-macronecine. An allylsilane-aldehyde ring closure formed the key step in the synthesis of these natural products.