Studies of the formation and stability of pentadienyl and 3-substituted pentadienyl radicals
摘要:
Pentadienyl radicals and their 3-methyl and 3-hydroxy derivatives were generated from the corresponding 1,4-pentadienes. The rates of hydrogen abstraction were studied by laser flash photolysis, and the bisallylic C-H bond dissociation energies were determined by photoacoustic calorimetry. Pentadienyl radicals were also generated by monoenergetic electron bombardment of 3-tert-butyl-1,4-pentadiene, and the radical's enthalpy of formation was deduced from the appearance energy of the tert-butyl cation. Evaluation of all recent data leads to recommended values of DELTA-H(f)-degrees (pentadienyl) = 49.8 +/- 1.0 kcal mol-1 and DH-degrees ((CH2 = CH)2CH) = 76.6 +/- 1.0 kcal mol-1. The EPR spectra of 3-methylpentadienyl and several other radicals were also examined. The effect of substituents on the stabilization energy of pentadienyl radicals was assessed, and pentadienyl radicals were compared with other delocalized polyenyl radicals.
Enantioselective Synthesis of cis-Fused Cyclooctanoids via Rhodium(I)-Catalyzed [4 + 2 + 2] Cycloadditions
作者:Brendan C. Lainhart、Erik J. Alexanian
DOI:10.1021/acs.orglett.5b00267
日期:2015.3.6
o]-type cycloadditions offer efficient, atom-economical routes to diverse complexcarbocycles. Recently, such transformations have emerged as unique strategies for medium ring carbocyclesynthesis. Despite the important developments in this area, however, highly enantioselective [m + n + o]-type processes accessing medium ring carbocycles have yet to be developed. Herein, a rhodium-catalyzed [4 + 2 + 2]
催化多组分[ m + n + o ]型环加成化合物提供了高效,原子经济的途径,可通往各种复杂的碳环化合物。最近,这种转化已成为中环碳环合成的独特策略。尽管在该领域取得了重要进展,但是,高度对映选择性[ m + n + o进入中环碳环化合物的]型过程尚未开发。在本文中,报道了铑催化的烯丙二烯与丙二烯的[4 + 2 + 2]环加成反应,从而能够直接立体选择性地合成顺式融合的环辛烷类化合物。这些环加成成功地用于各种π组分,并证明了在[4 + 2 + 2]过程中高水平对映选择性的潜力。
Studies towards Simalikalactone D and Quassimarin: Construction of an Advanced Pentacyclic Intermediate
作者:Tony K. M. Shing、Xue Y. Zhu、Yeung Y. Yeung
DOI:10.1002/chem.200305158
日期:2003.11.21
target molecules simalikalactone D and quassimarin, has been synthesized from (S)-(+)-carvone in 21 steps and with an overall yield of 12 %. The synthesis is efficient, stereocontrolled, enantiospecific, and chirality productive, creating eight new chiral centres in pentacycle, and should provide opportunities for rapid access to simalikalactone D analogues and other bioactive quassinoids. The reaction
involving 1,3-diene, alkyne, and silylene to afford silicon-containing seven-memberedrings was established. In the presence of a rhodium catalyst bearing bis(diphenylphosphino)methane (DPPM), nona-1,3-dien-8-yne derivatives reacted efficiently at 80–110 °C with boryl(isopropoxy)silane or boryl(diethyamino)silane, which reacts as the synthetic equivalent of silylene, to afford 1-silacyclohepta-2,5-dienes (2
建立了铑催化的[4 + 2 + 1]环加成反应,该反应涉及1,3-二烯,炔烃和亚甲硅烷基,以提供含硅的七元环。在带有双(二苯基膦基)甲烷(DPPM)的铑催化剂的存在下,壬基1,3-三烯-8-炔衍生物在80–110°C下与硼基(异丙氧基)硅烷或硼基(二乙氨基)硅烷有效反应,其作为亚甲硅烷基的合成当量反应,得到1-silacyclohepta-2,5-二烯(2,5-二氢-1 H-西勒平)。七元非共轭二烯的区域发散性和化学和立体选择性官能化是通过Cs 2 CO 3或铱催化剂介导的硼氢化作用实现的。
Concise, Enantioselective, and Versatile Synthesis of (−)-Englerin A Based on a Platinum-Catalyzed [4C+3C] Cycloaddition of Allenedienes
作者:Ronald Nelson、Moisés Gulías、José L. Mascareñas、Fernando López
DOI:10.1002/anie.201607348
日期:2016.11.7
A practical synthesis of (−)‐englerin A was accomplished in 17 steps and 11 % global yield from commercially available achiral precursors. The key step consists of a platinum‐catalyzed [4C+3C] allenediene cycloaddition that directly delivers the trans‐fused guaiane skeleton with complete diastereoselectivity. The high enantioselectivity (99 % ee) stems from an asymmetric ruthenium‐catalyzed transfer
A Versatile, Diels–Alder Reaction-Based Approach to Prenyleudesmane Diterpenoids: A Concise Total Synthesis of Sinupol
作者:Koichiro Ota、Hiroaki Miyaoka、Kazuo Kamaike
DOI:10.1055/s-0037-1610757
日期:2020.6
Herein, a concise strategy designed to provide general and diversifiable access to various prenyleudesmane terpenoids is described and utilized in the asymmetric synthesis of a biologically active prenyleudesmane diterpenoid, sinupol, which is accomplished in a seven-step procedure.