A General Synthetic Route to 6,6-Substituted-6H-dibenzo[b,d]pyrans from Dibenzofuran
摘要:
The reaction of dibenzofuran 1, lithium pieces (2.2 equiv), and TMEDA (2.2 equiv) in dry ether under reflux led to a solution of the corresponding C, O-dilithiated intermediate 2 which, upon treatment with different ketones or aldehydes (0.8 equiv) at -78 degrees C, afforded, after hydrolysis and dehydration, 6,6-substituted-6H-dibenzo[b,d]pyrans 3 in good yields. The reaction undergoes reductive ring opening and cyclization, and the intermediate diol 4e was isolated.
Substitution Controlled Functionalization of <i>ortho</i>-Bromobenzylic Alcohols via Palladium Catalysis: Synthesis of Chromenes and Indenols
作者:Lodi Mahendar、Gedu Satyanarayana
DOI:10.1021/jo402763m
日期:2014.3.7
transformation of simple ortho-bromobenzyl tertiaryalcohols to chromenes is presented. Their formation is believed to proceed via the formation of a five-membered palladacycle, which, in turn, involves in an intermolecular homocoupling with the second ortho-bromobenzyltertiary alcohol to yield the homo-biaryl bond followed by intramolecular C–O bond formation. Interestingly, when there is an allylic substituent
The palladium-catalyzedarylation of alpha,alpha-disubstituted arylmethanols with aryl halides proceeds not only via C-H bondcleavage at the ortho-position, but also via cleavage of the sp(2)-sp(3) C-C bond with the liberation of ketones (beta-carbon elimination) to give the corresponding biaryls. Both reactions appear to occur through common arylpalladium(II) alcoholate intermediates. The results
An Efficient Preparation of Chroman Derivatives from 3-Aryl-1-propanols and Related Compounds with 1,3-Diiodo-5,5-dimethylhydantoin under Irradiation Conditions
作者:Hideo Togo、Shusuke Furuyama
DOI:10.1055/s-0030-1258017
日期:2010.9
under irradiation with a tungsten lamp gave the corresponding chromanderivatives in good to moderate yields. The present reaction proceeds via the initial formation of an alkoxyl radical and the radical cyclization onto the aromatic ring, followed by the oxidation of the formed radical intermediate with DIH to provide the chromanderivative. The same treatment of o-biphenyldimethylcarbinol, o-phenylbenzoic
An efficient Pd-catalyzed domino reaction of α,α-dialkyl-(2-bromoaryl)methanols to 6,6-dialkyl-6H-benzo[c]chromenes is presented. Their formation can be explained via a five membered Pd(II)-cycle that efficiently involves a domino homocoupling with the second molecule, β-carbon cleavage, and finally intramolecular Buchwald–Hartwig cyclization. This domino process effectively involves breaking of five
提出了α,α-二烷基-(2-溴芳基)甲醇有效的钯催化多米诺反应为6,6-二烷基-6 H-苯并[ c ]色烯的反应。它们的形成可以通过一个五元的Pd(II)循环来解释,该循环有效地涉及与第二个分子的多米诺骨牌同质偶联,β碳裂解以及最后的分子内布赫瓦尔德-哈特维格环化。这种多米诺骨牌工艺实际上涉及打破五个σ键(2C–Br,2O–H和C–C)和形成两个新的σ键(CC和C–O)。这种机理途径是前所未有的,并进一步说明了过渡金属催化的作用。
Synthesis and X-Ray Crystal Structure of Cynandione B Analogues
作者:Lisa P. T. Hong、Jonathan M. White、Christopher D. Donner
DOI:10.1071/ch11364
日期:——
The synthesis of analogues of cynandione B, a phenolic acetophenone from Cynanchum taiwanianum, is described. The one-step conversion of benzochromenones to the heptacyclic spiroacetal core of cynandione B using methylmagnesium bromide is investigated and structural requirements for this novel transformation established. X-ray crystal structure analysis has established the relative configuration in