Jie Zhu

Stereospecific total synthesis of (−)-kjellmanianone and a revision of its absolute configuration

A fully stereocontrolled total synthesis of naturally occurring kjellmanianone 1 has been accomplished starting from tricyclo[5.2.1.02,6]decadienone 2-carboxylic ester 2. The key steps in this approach to 1 include Bartons halodecarboxylation methodology, nucleophilic epoxidation to introduce the hydroxy group and ultimately, a cycloreversion by using flash vacuum thermolysis. The R configuration of synthetic (−)-kjellmanianone was unequivocally established by an X-ray diffraction analysis of its precursor 6, implying that the previously assigned absolute configuration of (+)-kjellmanianone needs to be revised.

A stereo-and enantioselective approach to clavulones from tricyclodecadienone using flash vacuum thermolysis

Abstract The stereo- and enantioselective synthesis of clavulones 6 and their analogues 48 is described. γ-Hydroxycyclopentenones (−)- 13 and 44 , which are key intermediates in this approach, are obtained from enantiopure endo-tricyclo[5.2.1.02,6]decadienones (+)- 14 and (+)- 20 in 6 and 8 steps, respectively. Crucial steps are the reductive epoxy ring opening in compounds (+)- 25 and 39 to give the corresponding diols (+)- 27 and 40 , and the thermal cycloreversion of tricyclodecenones (+)- 27 and 41 , using the technique of flash vacuum thermolysis (FVT). The synthesis of enantiopure (−)- 13 represents a formal total synthesis of clavulones 6 . The synthesis of clavulone analogues (−)- 48E and (−)- 48Z (X = CH2OH) is completed by condensation of 44 with aldehyde 45 followed by elimination of water and removal of the protective THP-group.

Total synthesis of (−)-kjellmanianone from tricyclodecadienone. A revision of its absolute configuration

Abstract A stereocontrolled total synthesis of the naturally occurring cyclopentenoid (−)-kjellmanianone 8 has been accomplished starting from enantiopure (+)-tricyclo[5.2.1.02,6] decadienone 2-carboxylic ester 5 . Key steps in this approach to 8 include Bartons halodecarboxylation of 17 followed by methoxylation to produce 20 , nucleophilic epoxidation of enolacetate 26 to introduce the α-hydroxyketone moiety and thermal fragmentation of 27 using flash vacuum thermolysis (FVT) to give 8 . The R configuration of synthetic (−)-kjellmanianone was unequivocally established by an X-ray diffraction analysis of its precursor 27 , implying that the previously assigned absolute configuration of (+)-kjellmanianone is incorrect.

Synthesis of 6-functionalized tricyclodecadienones using Barton's radical decarboxylation reaction. Generation of tricyclo[5.2.1.02,6]decatrienone, a norbornene annulated cyclopentadienone

Abstract An effective synthesis of 6-functionalized endo-tricyclo[5.2.1.02,6]deca-4,8-dien-3-ones 7 starting from carboxylic acid 6 has been accomplished whereby the chemical scope of the tricyclodecadienone system 1 as a synthetic equivalent of cyclopentadienone has been expanded. Bridgehead bromide 7d gives upon treatment with base access to norbornene annulated cyclopentadienone 10 which rapidly undergoes either regioselective nucleophilic addition or Diels-Alder cyclization depending on the applied reaction conditions.

Generation and characterization of tricyclodecatrienone, a norbornene annulated cyclopentadienone

An effective synthesis of endo-6-bromo-tricyclo[5.2.1.02,6]deca-4,8-dien-3-one 3d is realized starting from carboxylic acid 2 applying Bartons halodecarboxylation methodology. Mild basic treatment of 3d leads to quantitative formation of tricyclo[5.2.1.02,6]decatrienone 5 which rapidly undergoes either regioselective nucleophilic addition or Diels-Alder cyclization depending on the applied reaction conditions.

A facile approach to norbornene-annulated cyclopentenones, a novel class of tricyclodecadienones

Abstract An efficient synthesis of norbornene annulated cyclopentenones 5 and 18 starting from readily available tricyclodecadienone carboxylic acid 2a is described. Parent tricyclo[5.2.1.02,6]decadi-2(6),8-ene 5 , an hitherto unknown compound, has been obtained in good yield by subjecting bromide 7b to base induced elimination or by oxidative deselenylation of 7c . 5-Substituted analogues 18 are conveniently obtained from phenylselenide 3c by stereoselective conjugate cuprate addition followed by oxidative elimination of the seleno group. Dehydrobromination of epoxy bromide 21 affords norbornene-annulated cyclopentadienone 22 which immediately undergoes stereoselective 1,4-addition at the strained C2–C6 enone moiety to give 23 . These novel norbornene annulated cyclopentenones can be considered as the synthetic equivalent of 2-cyclopentynones.

Synthesis of Cephalosporin‐Type Antibiotics by Coupling of Their β‐Lactam Nucleus and Racemic Amino Acid Side Chains Using a Clathration‐Induced Asymmetric Transformation

The cephalosporin-type antibiotics Cephalexin, Cephradine and Cefadroxil have been prepared by coupling of their β-lactam nucleus and racemic amino acid side chain precursors. The initially obtained mixture of cephalosporin epimers is subjected to a clathration-induced asymmetric transformation which results in the epimerization of the epi-cephalosporin into the cephalosporin with the correct diastereomeric configuration.