Rhodium-catalysed isomerisation/formal 1,3-dipolar cycloaddition cascades to fused-ring heterocycles

Abstract

Fused ring heterocycles were synthesised via the rhodium catalysed isomerisation/regio and stereoselective 1,3-dipolar cycloaddition cascades in good yields.

Crown Ether Base: Highly Active, Regioselective and Reusable Catalytic Systems for Double Bond Migration in Allylic Compounds

“…This reaction has also been used for the unmasking allylic protecting groups ,. Additionally, double bond migration is a key step of two‐ or multistep strategies, such as isomerizations: ‐Claisen rearrangements, ‐RCM, −1,3‐dipolar cycloaddition and other tandem reactions and cascades . As the catalysts of the double bond migration metals on supports (e. g., Pd / C , Rh / C ), Brønsted or Lewis acids (e. g., HClO 4 , H 2 SO 4 , zeolites), transition metal complexes ( Ti , Zr , V , Cr , Mo , Fe , Ru , Os , Co , Rh , Ir , Ni , Pd , Pt ) and various organic and inorganic bases which have been used up till now.…”

Synthesis of Heterocycles through Transition‐Metal‐Catalyzed Isomerization Reactions

“…This is in accordance with the findings by Cai et al that R has to be bulky for induction of high enantioselectivity. [27] Transition metal-catalyzed isomerization has also proven useful for the generation of azamethine ylides 64 from N-allyl-proline methylesters 62 for 1,3-dipolar cycloadditions with dipolarophiles 63 (Scheme 12, selected examples), as reported by Gorman et al [33] Upon subjection of 62 to Wilkinson's catalyst (10 mol %) in refluxing toluene, the azomethine ylides 64 underwent 1,3-cycloadditions with a range of dipolarophiles to afford the products 65 in moderate to excellent yields and excellent diastereoselectivities. Thus, 65 a and 65 b were obtained in 91 and 50 % yield, respectively, indicating that the reaction occurred via an endo transition state of the anti-dipole 64.…”

“…Transition metal‐catalyzed isomerization has also proven useful for the generation of azamethine ylides 64 from N ‐allylproline methylesters 62 for 1,3‐dipolar cycloadditions with dipolarophiles 63 (Scheme , selected examples), as reported by Gorman et al 33. Upon subjection of 62 to Wilkinson’s catalyst (10 mol %) in refluxing toluene, the azomethine ylides 64 underwent 1,3‐cycloadditions with a range of dipolarophiles to afford the products 65 in moderate to excellent yields and excellent diastereoselectivities.…”

Sequential one-pot three component rhodium-catalysed isomerisation/1,3-dipolar cycloaddition cascades to fused-ring heterocycles

“…11,12 We have recently reported the rhodium catalysed isomerisation of N-allyl proline methylester to generate azomethine ylides. 13 In this communication we report a novel three component rhodium catalysed isomerisation/1,3-dipolar cycloaddition cascades to generate fused-ring heterocycles with formation of three new bonds and four stereocentres using either acylic allylamines e.g. N-methylallylamine (Scheme 1a) or cyclic allylamines e.g.…”

“…We have identied Rh(PPh 3 ) 3 Cl as an effective catalyst for similar transformation. 13 Initially we carried out the cascade reaction of 2-bromoacetophenone 1 (1 mmol) with N-methylallylamine (1 mmol) and triethylamine (1 mmol) in toluene (20 mL) at room temperature until the alkylation was completed as shown by TLC, followed by addition of N-methylmaleimide (1 mmol) and (PPh 3 ) 3 RhCl (10 mol%) at 110 C for 8 h which afforded cleanly the cycloadduct 3 (Table 1 entry 1) in 73% yield. The relative stereochemistry of the cycloadduct 3 was assigned using n.O.e.…”