Macrocycle rearrangement

Trost (2004) plan for amphidinolide P step 15 (macrocyclization-rearrangement)... 

The synthesis of homoporphyrins in which one methine bridge of the parent porphyrin is extended to a two-carbon bridge is one of the earliest and simplest examples of an expanded porphyrin.3a b>4 The synthesis of homoporphyrin 4 is based on the ability of N-alkylated porphyrin 1 to undergo nickel-induced rearrangement to form an expanded macrocycle 2. De-metalation of 2 by means of concentrated hydrochloric acid yields the cyclically conjugated [20]porphyrin(2.1.1.1) 4 and a macrocyclic side product 3 in which the cyclic conjugation is interrupted. 

Keywords Medium-sized ring lactams. Macrocyclization. Ring expansion. Rearrangement, Fragmentation... 

Jautze S, Seiler P, Peters R (2007) Macrocyclic ferrocenyl-bisimidazoline palladacycle dimers as highly active and enantioselective catalysts for the Aza-Claisen rearrangement of Z-conflgured A-para-methoxyphenyl trifluoroacetimidates. Angew Chem Int Ed 46 ... 

In an alternative synthetic procedure, the Ni(n) complex of the depro-tonated form of (81) undergoes rearrangement on heating in water (at 100°C) at pH 5 over 6 hours. Addition of iodide ion and adjustment of the pH to 10 results in precipitation of the corresponding macrocyclic complex (77) as its iodide salt. More recently, the related acid-catalyzed... 

Only two general methods have been developed for the synthesis of the macrocyclic annulenes.9 The first of these, developed by Sondheimer and co-workers, involves the oxidative coupling of a suitable terminal diacetylene to a macrocyclic polyacetylene of required ring size, using typically cupric acetate in pyridine. The cyclic compound is then transformed to a dehydroannulene, usually by prototropic rearrangement effected by potassium i-butoxide. Finally, partial catalytic hydrogenation of the triple bonds to double bonds leads to the annulene. 

Phase-transfer catalysis can be used to mimic high dilution reaction conditions and has been utilized to good effect in the synthesis of large ring lactones [67J. Macrocyclic nitrolactones have also been obtained by rearrangement of 2-(3-hydroxy-propyI)-2-nitrocycloalkanones using a stoichiometric amount of tetra-n-butyl-ammonium fluoride [68]. 

J K mol and At.j/Atj = 0,016 result from the T-jump work (all data at 25°C in 3.0 M LiC104)." It is apparent then that the first step is rate determining in the establishment of the overall equilibrium. This presumably arises because the trans, cis rearrangement of the macrocyclic ligand occurs at this stage. Two possible free energy profiles are illustrated in Fig. 7.3. ... 

Themal treatment of the dimeric species 279 brings about a rearrangement to tetramer 281 (equation 56). The structure of 281 can be characterized by H, C H, P H and Li NMR spectroscopies. Recrystallization of 281 from toluene yields solvated crystals of formula 281-3PhMe, which show a core 12-membered macrocycle of C, P and Li atoms according to XRD crystallography ... 

---