NUCLEOPHILIC-ADDITION TO TUNGSTEN ETA(4)-2-(METHOXYCARBONYL)-1,3-PENTADIENE CATIONS - CONTROL OF NUCLEOPHILIC REGIOCHEMISTRY BY THE DIENE CONFORMATION

Citation
Mh. Cheng et al., NUCLEOPHILIC-ADDITION TO TUNGSTEN ETA(4)-2-(METHOXYCARBONYL)-1,3-PENTADIENE CATIONS - CONTROL OF NUCLEOPHILIC REGIOCHEMISTRY BY THE DIENE CONFORMATION, Organometallics, 13(10), 1994, pp. 4082-4091
Citations number
36
Categorie Soggetti
Chemistry Inorganic & Nuclear","Chemistry Inorganic & Nuclear
Journal title
ISSN journal
02767333
Volume
13
Issue
10
Year of publication
1994
Pages
4082 - 4091
Database
ISI
SICI code
0276-7333(1994)13:10<4082:NTTE>2.0.ZU;2-H
Abstract
Treatment of CpW(CO)3(eta1-vinylpropargyl) (1) with CF3SO3H in 1.2 equ imolar proportion in Et2O at -78-degrees-C, followed by addition of CH 3OH, produced (CO)2(eta3-2-(methoxycarbonyl)-2,4-pentadien-1-yl) (2) i n good yield. Further treatment of 2 with CF3SO3H in cold diethyl ethe r (-78-degrees-C) generated an orange precipitate of a4-s-trans-2-(met hoxycarbonyl)-1,3-pentadiene)]BF4 (3a), which was characterized by H-1 and C-13 NMR spectra. Above -10-degrees-C, this cation underwent an i rreversible isomerization to the more stable s-cis-eta4-diene conforme r 3b. The sites of nucleophilic addition to these two conformers are d istinct for most nucleophiles. For 3a, hard nucleophiles such as water , alcohols, thiols, and amines added exclusively at the =C(delta)HMe c arbon, whereas organocopper reagents preferred the C(alpha)H2 carbon t o give Michael reaction products. For 3b, nucleophiles regardless of t heir natures all add unambiguously at the C(alpha)H2 carbon. The disti nct nucleophilic regiochemistries of these two eta4-diene conformers a re discussed. To demonstrate the synthetic utility of these nucleophil ic additions, we performed demetalation of several allyl products deri ved from 3a and 3b.