A new route to tropanes

Metal-Assisted Cycloaddition Reactions in Organotransition Metal Chemistry

“…Schemes 24 and 25). 415,416,420,[657][658][659][660][661][662][663][664][665] in particular have strongly contributed to the development of the methodology. The use of Fe 2 (CO) 9 to reductively dehalogenate the R,R′-dibromo ketones has the advantage that through coordination to iron, a great variety of oxyallyl cations 180 (cf.…”

Pyrroles as Dienes in (4+3) Cycloadditions

“…29 Other reductive methods that produce iron or zinc oxyallylic cations reacted with 1e to give only Friedel-Crafts products. [30][31][32] Pyrroles bearing electron-withdrawing R 1 groups on nitrogen are less nucleophilic, and (4+3) cycloadditions can proceed with more electrophilic oxyallyl cations generated under a wider range of reducing conditions, including Fe 2 (CO) 9, 25, 33,34 Zn/Cu, 17,27,28,36 Zn/B(OEt) 3 , 37,38 and Et 2 Zn. 39,40 The resulting cycloadducts having electron-withdrawing groups on the aza-bridge are also more stable under acidic conditions.…”

“…35 Scheme 8 shows the results of cycloadditions with pyrroles bearing electron-deficient R 1 groups. 27,28,33,34,36,39,41,42 The ranges in yields shown are due to different results obtained by different reducing methods. In some cases, the yields varied even by using the same reductive methods, because the reaction conditions were further optimized.…”

“…35 In 2008, the Perlmutter group enantioselectively desymmetrized 42 in an asymmetric synthesis of the cancer MDR reversal agent, (+)-pervilleine C, 45 and in 2010 Hodgson and co-workers reported a synthesis of (±)-peduncularine from 42. 43 Scheme 7 (4+3) Cycloadditions of N-(electron-rich group)-substituted pyrroles [29][30][31] Scheme 8 (4+3) Cycloadditions of N-(electron-deficient group)-substituted pyrroles 27,28,33,34,36,39,41,42 Br O Br 39 (68%) 33 F. Hu et al…”

New chemical and stereochemical applications of organoiron complexes

“…For instance, 212 underwent [3 + 4] cycloaddition with open-chain dienes, producing substituted 4-cycloheptenones [ 401 ]. In addition, the cycloaddition of cyclic dienes including cyclopentadiene [ 401 , 402 ], and heteroaromatics such as pyrroles [ 401 , 403 ] and furans [ 401 , 404 ], gives bridged ketone systems. The reaction with furans proceeds by a concerted process, with the regioselectivity controlled by the frontier molecular orbitals of the two reactants [ 405 ].…”