Hexamethylene tetramine hydrotribromide is found to be superior to pyridine hydrotribromide when compared with the rate of reaction and chemoselectivity for the regioselective cyclisation of a number of ortho-cyclohexenyl phenols 1(a-j) to 3-bromo-2,4-propano-chromans 2(a-j).
Molybdenum(II)-Catalyzed Allylation of Electron-Rich Aromatics and Heteroaromatics
作者:Andrei V. Malkov、Stuart L. Davis、Ian R. Baxendale、William L. Mitchell、Pavel Kočovský
DOI:10.1021/jo982178y
日期:1999.4.1
The stable, readily available molybdenum(II) complexes [Mo(CO)(4)Br-2](2) (B) and Mo(CO)(3)(MeCN)(2)(SnCl3)Cl (C) have been found to catalyze C-C bond-forming allylic substitution with electron-rich aromatics (e.g., 15 + PhOMe --> 62) and heteroaromatics (e.g., 15 + 36 --> 88) as nucleophiles under mild conditions (room temperature, 30 min-3 h). Remarkable is the para-selectivity for anisole, whereas phenol tends to favor ortho-substitution in certain instances. Mechanistic and stereochemical experiments are indicative of Lewis-acid catalysis rather than a metal template-controlled process.
A number of ortho-cyclohexenyl phenols 2(a-i) have been cyclised by treatment with one equivalent of m-chloroperoxybenzoic acid in refluxing benzene for 4 h to furnish linearly fused 1-hydroxy-1,2,3,4,4a,9a-hexahydrodibenzofurans 3 (a-i) (70-80%) and bicyclic 3-hydroxy-1,3-ethanochromans 4(a-f) (10-20%). Products 3(a-i) were oxidised with 2,3-dichloro-5,6-dicyano-1 ,4-benzoquinone (excess) in refluxing dry xylene for 6 h to give 2,3-dihydrodibenzofuran-1 (2H)-ones 6(a-i) (85-95%).
<i>N</i>-IODOSUCCINIMIDE MEDIATED REGIOSELECTIVE HETEROCYCLIZATION OF <i>o</i>-CYCLOHEX-2′-ENYL PHENOLS
作者:K. C. Majumdar、P. K. Basu
DOI:10.1081/scc-120015388
日期:2002.1.1
A number of 3,4-benzo-9-iodo-2-oxabicyclo[3.3.1]nonanes (2a-f) are synthesized in excellent yields by regioselective heterocyclization of o-cyclohex-2'-enyl phenols (1a-f) with N-iodosuccinimide in acetonitrile at 0-5degreesC.