New Reaction Pathways for Fischer Carbene Complexes:  [6 + 3] Cycloaddition of Chromium Alkenyl Carbene Complexes with Fulvenes

Electronic Structure and Reactivity of Metal Carbenes

“…They have been widely used in synthetic reactions [37,[51][52][53][54][55][56][57][58] and show a very good reactivity especially in cycloaddition reactions [59][60][61][62][63][64]. As described above, Fischer-type carbene complexes are characterized by a formal metalcarbon double bond to a low-valent transition metal which is usually stabilized by p-acceptor substituents such as CO, PPh 3 or Cp.…”

[6+3] Cycloaddition of Fischer aminocarbene complexes: An efficient annulation of fulvenes to indene derivatives

“…Further interest of the reaction herein described can be envisaged as follows: (i) the unusual strategy of constructing the indene skeleton in the sense that most procedures are based by far on the annulation of the cyclopentene unit into the benzo ring, while the present work reports an easy benzannulation of the fulvene system, thus permitting to incorporate functionality into the aromatic domain [12], (ii) biological properties, e.g., as dopamine receptors ligands, have been reported for some amino substituted 2,3-dihydroindenes [13], (iii) since compounds 5 still maintain the reactive fulvene (CO) 5 unit they seem to be excellent candidates to produce extended polycyclic systems, a hypothesis that was demonstrated feasible in the case of alkenyl(alkoxy)carbenes [4].…”

“…Recently, we found that alkenyl(alkoxy)carbenes react with pentafulvenes, a particular type of polar system due to a unique C@C bond conjugation pattern, at 80°C in MeCN to produce efficiently indene derivatives [4]. This process was regarded as the first [6 + 3] cyclization of Fischer carbene complexes [5].…”

New heterocyclization reactions with Fischer carbene complexes

“…Thus, the reaction of chromium alkenyl alkoxycarbene complexes with 6-acetoxyfulvene in acetonitrile at 80ºC generated the substituted indenes 72 as a mixture of tautomers (Scheme 23). 17 Remarkably, 6-acetoxyfulvene reacted with alkenyl aminocarbene complexes as well, despite their well-known considerably less reactivity in nucleophilic additions. Moreover, the reaction of alkoxyalkenyl carbenes with alkyl and alkenyl fulvenes in acetonitrile at 80ºC furnished also the [6+3] cycloadducts, which after acid ARKAT hydrolysis were transformed into indanones 73 in good overall yields.…”