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Palladium‐Catalyzed Bicyclization of 2‐Bromo‐1,6‐dienes and ‐1,6‐enynes to 5‐Membered‐Ring‐Annelated Vinylcyclopropane Derivatives
Author(s) -
Steinig Arno G.,
de Meijere Armin
Publication year - 1999
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199906)1999:6<1333::aid-ejoc1333>3.0.co;2-g
Subject(s) - chemistry , diene , substituent , bicyclic molecule , medicinal chemistry , allylic rearrangement , moiety , intramolecular force , alkene , hydride , palladium , stereochemistry , catalysis , organic chemistry , hydrogen , natural rubber
Palladium‐catalyzed cyclizations of the 2‐bromo‐1,6‐diene 6 with an acetoxymethyl substituent on the bromoalkenyl moiety did not only lead to the expected 1‐acetoxymethyl‐1,3‐diene 40 but also to the bicyclic vinylcyclopropane 35 , the 1,3‐diene 36 and the triene 37 (a dendralene). All these compounds result from an initial 5‐ exo‐trig cyclization of the 2‐bromo‐1,6‐diene. By proper choice of the reaction conditions (ligand, base, allylic leaving group) each of these compounds could be formed selectively. Small amounts (3–5%) of the isomerized 1‐acetoxymethyl‐1,3‐diene 38 and the 6‐ endo product 39 were also isolated. With the acetoxymethyl substituent on the alkenyl moiety (compound 27 ) only the 1,4‐diene 44 was formed. The related 1,6‐enyne 57 with a methoxycarbonyloxymethylene substituent on the triple bond gave in 36% yield the 2,3‐bis(bicyclo[3.1.0]hex‐1‐yl)‐substituted 1,3‐butadiene 63 , which can be regarded as a dehydrodimer of the vinylcyclopropane 35 . The presumption that the formation of 63 involves the alkenylpalladium species 65 was supported by its successful inter‐ as well as intramolecular trapping with formate as a hydride source to yield the vinylcyclopropane 35 . The reaction pathways leading to the vinylcyclopropane derivatives 35 and 63 have in common that an alkylpalladium species rather undergoes a 3‐ exo‐trig cyclization than an internal rotation followed by a β‐hydride elimination.