Hirsutene and Δ 9(12) Capnellene. D. P. Curran (1986) Presenter: Mehdi Moemeni
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1 irsutene and Δ 9(12) Capnellene D. P. Curran (1986) Presenter: Mehdi Moemeni
2 Back Ground of Radical Structure In a modern context the first organic free radical identified was triphenylmethyl radical. This species was discovered by Moses Gomberg in 1900 at the University of Michigan. C Gomberg, M. J. Am. Chem. Soc. 1900, 22,
3 Radical Reactions Radical chain reactions have three distinct phases: 1) initiation, 2) propagation, and 3) termination. Initiation X 2 (heat or light) 2X Propagation R + X R + X R + X 2 RX + X Termination R + X RX Smith, M. B.; March, J. Advanced rganic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley, ISBN
4 Baldwin s Rules Y Z Z Y Y Z Z Y X X X X Exo-Tet Endo-Tet Exo-Trig Endo-Trig Y Z Z Y X Exo-Dig X Endo-Dig - Tetrahedral for sp3 carbon - Trigonal for sp2 carbon - Digonal for sp carbon Baldwin J. E. J. Chem. Soc., Chem. Commun. 1976, 18, 734.
5 Radical Reactions Examples Br n-bu 3 Sn 6-exo-trig PhC 3 t-bu h, (62%) radical cyclization n-bu 3 Sn Ketone olefination Copacamphene Sativene 5 4 stereoisomeric ratio of 4 to 5 (2:3) Bakuzis, P.; Campos,..S.; Bakuzis, M. L.F. J. rg. Chem. 1976, 41, 3261.
6 Radical Reactions in Examples Et I n-bu 3 SnCl (0.1 equiv.), NaCNB 3 (2.0 equiv.), h TF, 25 C Et 5-exo-trig Et SiMe 3 radical cyclization TBS C 5 11 TBS TBS (trimethylsilyl)-1-octen-3-one (7equiv.) intermolecular trapping Et Et Et TBS 140 C, Brook Rearrangement TBS SiMe 3 n-bu 3 Sn TBS SiMe 3 11 Me 3 Si C C C 5 11 C 2 (+) prostaglandin F 2 Stork, G.; Sher, P.M.; Chen,. L. J. Am. Chem. Soc. 1986, 108, 6384.
7 Radical Reactions in Examples N Br Br N Sn n-bu 3 N N N- bromosuccinimide (2.0 equiv) 13 C 2 Cl 2, 0 C (83%) 14 AIBN (cat.) Ph, reflux 15 (88%) NC N N CN AIBN: 2,2 -azobisisobutyronitrile intermolecular trapping N (-n-bu 3 Sn ) -ellimination N Sn n-bu Keck, G.E.; Yates, J.B. J. rg. Chem. 1982, 47, 3590; Keck, G.E.; Enholm, E.J.; Yates, J.B.; Wiley, M.R. Tetrahedron 1985, 41, 4079.
8 Radical Reactions in Examples ClN (nitrosyl chloride) N h abstraction atom N (nitric oxide) N tautomerization 22 N Barton, D..R.; Beaton, J.M.; Geller, L.E.; Pechet, M. M. J. Am. Chem. Soc. 1960, 82, 2640; Barton, D.. R.; Beaton, J.M.; Geller, L.E.; Pechet, M.M. ibid. 1961, 83, Barton, D.. R. Pure & Appl. Chem. 1968, 16, 1; Barton, D.. R. Aldrichimica Acta 1990, 23, 3.
9 Radical Reactions in Examples Ac Ac CIN N pyr., 25 C corticosterone acetate h PhC 3, 32 C (nitrite ester photolysis) (-N) Ac Ac -atom abstraction Barton, D..R.; Beaton, J.M. J. Am. Chem. Soc. 1960, 82, 2641; Barton, D.. R.; Beaton, J.M. ibid. 1961, 83, 4083.
10 Radical Reactions in Examples Ac Ac 29 -atom abstraction 28 N N Ac tautomerization N Ac 30 N 2 nitrous acid 31 (20% yield from SM) Ac Barton, D..R.; Beaton, J.M. J. Am. Chem. Soc. 1960, 82, 2641; Barton, D.. R.; Beaton, J.M. ibid. 1961, 83, aldostrone 21-acetate
11 Back Ground of irsutene In 1947, eatley and co-workers reported that (+)-hirsutic acid produced by the filamentous fungus Stereum hirsutum. This is derived, in vivo, from the (+)-hirsutene. - First total synthesis : Nozoe, S; Tetrahedron Lett. 1976, 17, First total synthesis by Radical Reactions: Curran, D. P.; Rakiewicz, D. M. J. Am. Chem. Soc. 1985, 107, 1448 Tetrahedron 1985, 41, First Asymmetric total synthesis: ua, D..; Sinai-Zingde, G,; Venkataraman, S. J. Am. Chem. Soc., 1985, 107, irsutene (a linear triquinane)
12 Back Ground of Capnellene Capnellene (a linear triquinane) Capnellene is a naturally occurring hydrocarbon derived from Capnella imbricata, a species of soft coral. Capnellene derivatives and hirsutenes, demonstrate antibacterial and antitumor properties with pharmacological potential. - First total synthesis: Paquette, L; J. Am. Chem. Soc. 1985, 107, First total synthesis by Radical Reactions : Curran, D.P.; Chen, M.. Tetrahedron Lett. 1985, 26, First Asymmetric total synthesis: Meyers, A; Bienz,S; J. rg. Chem., 1990, 55,791.
13 Back Ground Dennis Patrick Curran Professor at University of Pittsburgh Well known for work in the interface of radical chemistry and organic synthesis
14 irsutene
15 Retrosynthetic Analysis and Strategy 5-exo-dig hirsutene radical cyclization 32 5-exo-trig radical cyclization TP 35 M S N 2 I lactone opening 36 C-C bond formation trans disubstituted cyclopentene Curran, D. P.; Rakiewicz, D. M. J. Am. Chem. Soc. 1985, 107, 1448 Curran, D. P.; Rakiewicz, D. M. Tetrahedron 1985, 41, 3943
16 Total Synthesis TBS 1- NaB 4, CeCl 3 (Luche reduction) Ac LDA, TF, -78 C 2- Ac 2, Et 3 N Then t-bume 2 SiCl MPA 39 C 3 Cl, reflux (Ireland ester enolate Claisen rearrangement) [3,3] Se Ph TF (62% from 37) PhSe 41 PhSeCl, C 2 Cl 2, -78 C Phenylseleno lactonization 40 TBS Curran, D. P.; Rakiewicz, D. M. J. Am. Chem. Soc. 1985, 107, 1448 Curran, D. P.; Rakiewicz, D. M. Tetrahedron 1985, 41, 3943
17 Se Ph Total Synthesis 42 (Selenoxide syn-elimination) 43 TP Br 44 Li naphthalenide, TF, -78 C (organolithium formation) then CuBr SMe 2 (organocuprate formation) then 43(50-75%) TP 45 C 2 1. PPTS, Et 2. LiAl 4 (64% overall) I 1. Me 3 Si Li (1.0 equiv) TF, 0 C CsF (78% overall) I 47 I 1. (Tf) 2 Pyr C 2 Cl 2, -10 C 2. n-bu 4 NI Ph, reflux (64% overall) 46 Curran, D. P.; Rakiewicz, D. M. J. Am. Chem. Soc. 1985, 107, 1448 Curran, D. P.; Rakiewicz, D. M. Tetrahedron 1985, 41, 3943
18 Reductive Litiation Li Br TP TP Li TP Naphtalenide LiBr Li TP C 2 45 Single regio and stereo isomer Freeman. J. rg. Chem. 1980, 45, 1294.
19 Total Synthesis I n-bu 3 Sn, AIBN (cat) 5-exo-trig radical cyclization Ph reflux (80%) NC N N CN 5-exo-dig radical cyclization AIBN: 2,2 -azobisisobutyronitrile n-bu 3 Sn ( )-hirsutene 51 Curran, D. P.; Rakiewicz, D. M. J. Am. Chem. Soc. 1985, 107, 1448 Curran, D. P.; Rakiewicz, D. M. Tetrahedron 1985, 41, 3943
20 Capnellene
21 Retrosynthetic Analysis and Strategy 5-exo-dig 5-exo-trig Capnellene radical cyclization radical cyclization X C Curran, D.P.; Chen, M.. Tetrahedron Lett. 1985, 26,4991
22 Total Synthesis ( )- norbornenone Baeyer- villiger oxidation acid-catalyzed rearrangement MeMgBr CuBr.SMe 2 TF, -20 C 60 DBU,TF, 25 C (66% from 147) I 59 I 2 Iodolactonization 58 C 2 Curran, D.P.; Chen, M.. Tetrahedron Lett. 1985, 26,4991
23 Acid catalyzed rearrangement
24 Total Synthesis 60 MgBr CuBr.SMe 2, TF, -20 C (S N 2 anti lactone opening) 61 C 2 LiAl 4 (80% from 150) MeS 2 Cl 2. NaI 3. Li. 2 N(C 2 ) 2 N 2 DMS, 25 C (43% from 152) Br 1. MeMgBr (excess) C 2 Me 1. Cr 3. aq. 2 S 4, (C 3 ) 2 C 2. C 2 N 2 ( 70% overall) Me 3 SiBr (90% overall) 64 Jones oxidatio 63 Curran, D.P.; Chen, M.. Tetrahedron Lett. 1985, 26,4991
25 Total Synthesis Br n-bu 3 Sn, AIBN(cat.) 5-exo-trig Ph 80 C (80% GC yield) radical cyclization 67 5-exo-dig radical cyclization n-bu 3 Sn )- 9(12) -Capnellene 68 Curran, D.P.; Chen, M.. Tetrahedron Lett. 1985, 26,4991
26 Conclusion Through the application of radical chemistry, valuable functional group transformations and challenging carbon-carbon bond construction can be achieved under usually mild reaction condition. Radical reactions are powerful, one-pot strategies for the synthesis of complex polycyclic molecules. Carbon-centered radicals are also highly reactive intermediates that add to carboncarbon π bonds via early, reactant-like transition states. Tandem or sequential radical cyclizations can offer exceedingly concise solutions to challenging problems in organic synthesis.
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CuI CuI eage lic R tal ome rgan gbr ommon
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