An approach to the core skeleton of lancifodilactone F

Two cycloaddition reactions were utilized for the construction of the 5,6,7-tricyclic skeleton of lancifodilactone F and buxapentalactone. A [2+2] ketene cycloaddition reaction was first used to set their adjacent all-carbon quaternary centers at the 5,6-ring junction. An arene-olefin meta-photocycloaddition reaction was then used to install the 6- and 7-membered rings concurrently.     

An approach to isoindole skeleton via ortho palladation

An acid-induced cyclisation of the products of vinylation of ortho palladated NN-dimethylbenzylamines by 3-buten-2-one (II) leads to isoindolinium derivatives (IV) as confirmed by an X-ray structural study.     

Two novel alkaloids with a unique fused hexacyclic skeleton from Daphniphyllum subverticillatum

Two novel major alkaloids, deoxycalyciphylline B (1) and deoxyisocalyciphylline B (2) with a unique fused hexacyclic skeleton, together with a quite recently reported alkaloid calyciphylline B (3), were isolated from the stem of Daphniphyllum subverticillatum. Their structures were established by spectral methods and chemical evidence, especially 2D NMR techniques. The structure of 1 was further confirmed by a single-crystal X-ray diffraction determination.     

Models of folate coenzymes 14: An alternate approach to the yohimbane skeleton

The anion of dimethyl homophthalate adds to imidazolinium and tetrahydropyrimidinium salts ($\text{2a,b}$) to yield imidazolidine and tetrahydropyrimidine adducts corresponding to methylenetetra-hydrofolate models ($\text{3a,b}$). These models transfer the carbon fragment 2-(MeOOC)C₆H₄CH(COOMe)CHXXX to tryptamine to give an enamino ester intermediate which is cyclized, in two steps to the yohimboid skeleton.     

A concise approach to the dalesconol skeleton

A rapid approach to the skeleton of dalesconol A and B, unprecedented immunosuppressants, has been achieved through a convergent strategy featuring a carbocation-mediated dearomatization-cyclization and a following one-pot consecutive operation.     

Sequential aminodiene Diels-Alder approach to the ergoline skeleton

Through a novel sequence of aminodiene Diels-Alder reactions, several substituted amidofurans were readily converted to tricyclic ketones in good yield. The formation of the tricyclic ketone system is the result of a ring opening and dehydration of a transient oxabicyclic adduct formed by an intramolecular Diels-Alder cycloaddition of an amidofuran with a cyclohexenone moiety tethered such that it participates in the cycloaddition as the 2pi component. A convenient way to construct the cyclohexenone is to make use of some aminodiene chemistry developed by Rawal. An angular carbomethoxy group is required in order to activate the olefin toward cycloaddition with Rawal's diene. The presence of this activating group not only prevents the isomerization of the advanced ergoline intermediate to a naphthalene but can also be leveraged for an oxidation to provide Uhle's ketone (13). The easily formed Kornfeld ketone analogue 25 was readily transformed into the corresponding triflate 41 by the action of triflic anhydride and a base. Oxidative addition of vinyl triflate 41 to Pd(0) and the ability of the resulting vinyl palladium species to undergo cross-coupling with terminal alkynes prompted us to devise an expeditious route to lysergic acid. Unfortunately, our inability to carry out a regioselective Heck reaction using vinyl triflate 41 and the methylene amino acrylate ester 48 thwarted the completion of the synthesis of lysergic acid.     

An approach to vindoline skeleton utilizing substituted methylenetetrahydrofolate (5,10-CHR-THF) models

Starting from a substituted methylenetetrahydrofolate model [4-(2-N(1)-tosyl-N(3)-methyl-4,4-dimethylimidazolidyl)-3-ketobutanoate], an efficient synthesis of the pentacyclic system corresponding to vindoline is described.     

Novel synthetic approach to the 8,10-dimethyl anti-syn-anti-perhydrophenanthrene skeleton

[reaction: see text] An efficient and highly stereocontrolled approach to the 8,10-dimethyl anti-syn-anti-perhydrophenanthrene carbon skeleton starting with the Wieland-Miescher ketone is described. The approach centers on a Diels-Alder-angular methylation-deoxygenation sequence.     

A facile two synthon approach to the camptothecin skeleton

A synthesis of deethyldesoxycamptothecin via the reaction of two readily accessible synthons is described. One of the synthons constitutes the ABC ring system of camptothecin, while the second provides all the C atoms of the rings D and E. The synthetic approach is suited for the total synthesis of camptothecin analogues.     

An approach to the skeleton of the securinega alkaloids. The total synthesis of (+/-)-securinine

[structure: see text]. The concise total synthesis of securinine in nine steps from readily available starting materials is described. Key steps of the synthesis include an addition of a silyloxyfuran to an in situ generated iminium ion and a novel ring closing metathesis reaction.     

Synthetic study of hetisine-type aconite alkaloids. Part 2: Preparation of hexacyclic compound lacking the C-ring of the hetisan skeleton

A hexacyclic compound 1, having almost the full hetisine-type aconite alkaloid framework lacking only the C-ring with an exo-methylene group, was synthesized from the intermediate 3 reported in the preceding paper. The synthesis involved the following key reactions the crucial conversion of 3 to 4, a stereoselective hydrocyanation reaction to obtain 5 from 4, and construction of the azabicyclic ring system (5→1).     

An expedient approach to internally functionalized chiral dendrimers: synthesis of a dendritic molecule incorporating furanoside skeleton

In an approach to chiral dendritic molecules, a dendrimer incorporating pentose units in the interior and hexose units in the periphery is built up on a 1, 3, 5-trisubstituted aromatic core by using 1,2:5,6-diisopropylidene glucose as the carbohydrate precursor and a 3, 5-disubstituted aromatic unit as the branching block. The carbohydrate moiety also provides internal functionalities in the form of hemiacetal moiety of the furanoside ring.     

Sequential pericyclic reaction of ene-diallenes: an efficient approach to the steroid skeleton

[reaction: see text] The one-pot construction of polycyclic aromatic systems from acyclic ene-bis(propargyl alcohols) was achieved through a tandem dual [2,3]-sigmatropic rearrangement/6pi-electrocyclic reaction/intramolecular [4 + 2] cycloaddition sequence. A steroidal compound was conveniently synthesized using the present method.     

Steroselective synthesis of the basic skeleton of aphidicolan diterpenes: synthetic approach to aphidicolin

The basic skeleton of aphidicolan-type diterpenes was stereoselectively synthesized via thermolysis of a benzocyclobutene.     

Inter- and intramolecular reductive coupling reactions: an approach to the phorbol skeleton

[reaction: see text] An expeditious convergent route to the ABC-tricyclic core of the phorbol esters is described. The chemistry capitalizes upon both inter- and intramolecular reductive coupling processes promoted electrochemically and via the use of samarium diiodide.     

Kopsifolines A, B, and C, indole alkaloids with a novel hexacyclic carbon skeleton from Kopsia

Three indole alkaloids, viz., kopsifolines A, B, and C, characterized by a novel carbon skeleton, were obtained from a Malayan Kopsia species and the structures established by spectroscopic analysis.     

An alternative synthesis of the 1-oxacephem skeleton

1-Oxacephem skeletons were constructed in a convergent manner starting from building blocks $\text{B}$ and $\text{C}$, which were easily prepared from penicillin and diketene, respectively, followed by intramolecular carbene insertion reaction of the resulting intermediate $\text{A}$.