Premium
Molybdenum‐Catalysed and ‐Mediated Cycloaddition Reactions: Efficient Synthesis of Complex Products from 1‐Oxa‐1,3‐dienes and Cyclotrienes or ‐tetraenes
Author(s) -
Schmidt Thomas
Publication year - 1997
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19971300404
Subject(s) - chemistry , cycloaddition , molybdenum , cycloheptatriene , catalysis , medicinal chemistry , selectivity , diene , stereochemistry , stereoselectivity , organic chemistry , natural rubber
Molybdenum‐mediated [6 + 2]‐cycloaddition reactions of unsaturated ketones to cyclotri‐ or ‐tetraenes, e.g. cyclohepta‐1,3,5‐triene or cyclooctatetraene, proceed under very mild conditions, in high yields and with excellent stereoselectivity starting from the appropriate dicarbonylbis[π 4 ‐(1‐oxa‐1,3‐diene)]molybdenum complexes. The stereochemistry of the product arising from the reaction of dicarbonylbis[π 4 ‐(5‐methylhex‐3‐en‐2‐one)]molybdenum with cyclohepta‐1,3,5‐triene allows one to deduce a stepwise mechanism for this addition. The reactants are fused, as would be expected from an exo ‐type approach, thus indicating an intermolecular attack of the cycloheptatriene. Tungsten oxadiene complexes are effective in analogous reactions at somewhat reduced reaction rates. Catalytic cycloadditions are observed in several cases when 1–5 mol% of the highly reactive dicarbonylbis[π 4 ‐( R ‐(+)‐pinocarvone)]molybdenum is employed as the catalyst. Cycloadducts are formed diastereospecifically in most cases. When cyclooctatrienes are employed as reactants, a sequence of electrocyclization of the triene and subsequent [4 + 2]‐cycloadditon occurs with high selectivity and efficiency, leading to a pentacyclic ketone. The product structure reveals an endo ‐type approach of the polyene in this case.