Platinum(II)-Catalyzed Generation and [3+2] Cycloaddition Reaction of α,β-Unsaturated Carbene Complex Intermediates for the Preparation of Polycyclic Compounds

Abstract

Pt(II)-catalyzed generation of unsaturated carbene complex intermediates from various propargyl ether derivatives based on electrophilic activation of alkynes was realized. These in situ generated unsaturated carbene complexes undergo [3+2] cycloaddition reaction with various vinyl ethers, leading to efficient formation of indoles, naphthols, and benzofuran fused with a five-membered ring in high yields.

Gold(I)‐Catalyzed Cycloisomerizations and Alkoxycyclizations of ortho‐(Alkynyl)styrenes

“…Then, using methanol and/or water as nucleophile a variety of functionalized indenes 10 with selected substitution at R 1 , R 2 and R 3 were synthesized (entries 7-19). As expected by the results obtained in the cycloisomerization in the absence of nucleophile the reaction tolerates both electron-withdrawing (entries 7-10) and electron-donating (entries [11][12] groups at the internal phenyl ring as well as a broad range of substituents at the triple bond including (hetero)aromatic (entries 7-14), (cyclo)alkyl (entries 15-18), and heteroatomic moieties (entry 19). All these reactions were completely selective and we did not observe the formation of additional products derived from other possible reaction pathways.…”

“…Therefore, we were pleased to find that, after some optimization, [42] we were able to obtain indene derivatives with good enantiomeric excess using the combination (S)-3,5-xylyl-MeOBIPHEP-(AuCl) 2 / AgOTs as catalyst in dichloromethane at -30 ºC (Table 6). Under these optimized catalytic conditions we found high yields and enantioselectivities for o-(alkynyl)styrenes 3a-e,6a-b where R 5 is an aromatic or heteroaromatic group (entries [1][2][3][4][10][11]. Interestingly, the possibility of increasing the enantiomeric excess of the final 8 products by a simple recrystallization has been demonstrated for indene 7b that we were able to isolate with 92% ee (entry 11).…”

“…[7] In contrast, the substitution pattern of the olefin plays a critical role in the cycloisomerization of ortho-(alkynyl)styrenes (Scheme 1). Thus, the skeletal rearrangement of o-(alkynyl)styrenes -substituted and mono-or non--substituted to produce naphthalenes through a 6-endo cyclization process has been described using complexes derived from several metals such as W, 2 Rh, [9] Ru, [9] Pd, [9][10][11] Pt, [9,11] Ag [12] or Au [9,13] as catalysts (Scheme 1a). Related cycloaromatizations of o-(alkynyl)biaryls also occurred allowing the efficient preparation of substituted phenanthrenes and other polycyclic heteroarenes.…”

Rhodium‐ and Platinum‐Catalyzed [4+3] Cycloaddition with Concomitant Indole Annulation: Synthesis of Cyclohepta[b]indoles

“…[10,11] Similarly, vinyl Fisher carbenes [12] or vinyl gold carbenes derived from propargylic esters [13] can also react with dienes to form various seven-membered rings. It was recently reported that vinyl metal carbenes could be conveniently generated from propargylic ethers tethered with a nucleophile for a [3+2] cycloaddition [14] and a synthesis of furans. [15] We envisioned that the vinyl metal carbene 2 , derived from 1 , would undergo a formal [4+3] cycloaddition [16] with diene 3 to afford the cyclohepta[ b ]indole 4 by either a cyclopropanation/Cope rearrangement sequence involving the divinyl-cyclopropane 5 , or an unusual [4+4] cycloaddition to form the eight-membered metallacycle 6 with subsequent reductive elimination.…”

“…[14,15] A low yield of 4a or no product, however, was observed using these catalysts (Table 1, entries 5–8). We suspect that the coordination of the bidentate diene 3a to PtCl 2 may reduce the acidity of the metal.…”