摘要:

Organic Syntheses via Transition Metal Complexes, 501). – 2H‐Pyrrole Complexes by a Stepwise Insertion of Alkynes and Isocyanides into MC Bonds of Carbene Chromium or Tungsten Complexes2H‐Pyrrole complexes6a, bare obtained in two step by [1+2+2] cycloaddition reactions of the carbene complex (CO)5WC(OEt)C6H5(1d), the alkyne EtO‐CCH (2) and isocyanides R1‐NC4a, b[R1= CH3,c‐C6H11). LnC(OEt)R1[LnM = Cr(CO)5, W(CO)5; R = C6H5, CH3] reacts with2to give 1‐metalla‐1,3‐dienes3a–d. (E)/(Z)‐3dand4yield6a, bvia 1‐aza‐1,2,4‐pentatriene complexes5, which are open‐chain precursors of6. 2H‐Pyrrole complexes11and14are synthesized in overall [2+1+2] cycloadditions withe reversed connectivity, or formation of 1‐chroma‐1,3‐dienes10and13by condensation of the methylcarbene complex1awith acid am

ISSN:0009-2940    

DOI:10.1002/cber.19911240132

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

Abstractα‐Silylated ketones5or10of high enantiomeric purity (ee ≥ 90%) are easily available by silylation or silylation/alkylation of ketones1or6, resp., according to the SAMP/RAMP hydrazone method. Reduction of5or10with L‐selectride™, followed by oxidative cleavage of the C–Si bond, leads tovic‐diols11–13with high diastereoselectivity (de ≥ 90%) and without racemization. The stereoselectivity of the reduction depends on the structure of the α‐silyl ketones5or10, the reducing reagents, an

ISSN:0009-2940    

DOI:10.1002/cber.19911240133

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe synthesis of epoxides3a–ris achieved in excellent yields by reaction of the α,β‐unsaturated ketones1a–c, 4,4′‐disubstituted (E)‐chalcones1d–o, and 2′‐hydroxy‐4‐substituted (E)‐chalcones1p–rwith isolated dimethyldioxirane (2a) (as acetone solution) and/or in situ generated ethyl(methyl)dioxirane (2b). This method constitutes a useful alternative to the Weitz‐Scheffer epoxidation (alkaline H2O2) of

ISSN:0009-2940    

DOI:10.1002/cber.19911240134

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

New O6Macrocycles with 2,2‐Bis(2‐furyl)propane UnitsThe macrocycles3aand6are prepared in29and 16% yield by cyclization of dilithiated 2,2‐bis(2‐furyl)propane (1) and 2,5‐bis[1‐(2‐furyl) 1‐methylethyl]furan (5), respectively, with ethyl N,N‐dime

ISSN:0009-2940    

DOI:10.1002/cber.19911240135

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

Rearrangements of 1,4,4‐ and 2,2,5‐Trimethylbicyclo[3.2.1]oct‐6‐yl Cations1,4,4‐Trimethylbicyclo[3.2.1]oct‐6‐yl cations (18) are generated from the tosylhydrazone7, by nitrous acid deamination of the amines6and8, and by acetolysis of the brosylates21and24. The product distributions are but slightly affected by the configuration (exovs.endo) of the leaving groups. The predominant product, 1,4,4‐trimethylbicyclo[3.2.1]octan‐exo‐6‐ol (11) is formed without significant redistribution of a 6‐2H label. The degenerate Wagner‐Meerwein rearrangement of the parent bicyclo[3.2.1]oct‐6‐yl cation is virtually eliminated by the presence of two methyl groups at C‐4. Enhanced conformational strain, raising the barrier to ring flipping, accounts for these observations. Minor products (12, 13) arise from a 7,6‐hydride shift of18, followed by Wagner‐Meerwein rearrangement. When the 2,2,5‐trimethylbicyclo[3.2.1]oct‐6‐yl cation (19) is generated directly from the tosylhydrazone17, the tertiary alcohol13is obtained as the major product. The conformational barrier to Wagner‐Meerwein rearrangement is compensated by the incipient

ISSN:0009-2940    

DOI:10.1002/cber.19911240136

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

Rearrangements of 5,5,6,6‐Tetraalkyl‐2‐norbornyl CationsWhen the 6,6‐dimethyl‐2‐norbornyl cation (9) is generated from the tosylhydrazone 5 by way of the diazonium ion8, a2H label is distributed equally between positions 1 and 2 of theexo‐alcohol10. The degeneracy of9, previously derived from solvolytic studies, is thus confirmed for the deaminative route. 5,5,6,6‐Tetramethyl‐2‐norbornanone (25) and tetracyclo[4.2.2.12,5.01,6]undecan‐3‐one (31) are prepared by using Diels‐Alder methodology. The corresponding tosylhydrazones26and32are employed as precursors for the 5,5,6,6‐tetramethyl‐2‐norbornyl and tetracyclo[4.2.2.12,5.01,6]undec‐3‐yl cations (11and12). Again, the distributions of2H labels are close to 1 : 1. The angular distortions expected from repulsive interactions of the methyl groups in11and from cyclobutane annulation in12do not affect the re

ISSN:0009-2940    

DOI:10.1002/cber.19911240137

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

3a‐Hydroxy‐6‐hydrindanones of type10and11can be obtained by acid‐catalyzed or Lewis acid‐promoted cyclization reactions of ene‐ketals of type6and7. The compounds described are interesting building blocks for biologically active heart

ISSN:0009-2940    

DOI:10.1002/cber.19911240138

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

ISSN:0009-2940    

DOI:10.1002/cber.19911240101

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY