Cobalt-Catalyzed Regioselective Carbocyclization Reaction of o-Iodophenyl Ketones and Aldehydes with Alkynes, Acrylates, and Acrylonitrile:  A Facile Route to Indenols and Indenes

Abstract

An efficient cobalt-catalyzed carbocylization for the synthesis of indenols and indenes and a new method for reductive decyanation are described. 2-Iodophenyl ketones and aldehydes 1a-g undergo carbocyclization with various disubstituted alkynes 2a-k in the presence of Co(dppe)I(2) and zinc powder in acetonitrile at 80 degrees C for 3 h to afford the corresponding indenol derivatives 3a-s and4a-m in good to excellent yields. For some unsymmetrical alkynes, the carbocyclization was remarkably regioselective, affording a single regioisomer. The cobalt-catalyzed carbocyclization reaction was successfully extended to the synthesis of indene derivatives. Thus, the reaction of 2-iodophenyl ketones and aldehydes (1) with acrylates H(2)C=CHCO(2)R (7a-d) and acrylonitrile H(2)C=CHCN (7e) proceeds smoothly in the presence of Co(dppe)Cl(2)/dppe and zinc powder in acetonitrile at 80 degrees C for 24 h to afford the corresponding indenes 8a-k and 9a-c in moderate to good yields. Interestingly, when 7e was employed for the carbocylization, reductive decyanation also occurred to give an indene derivative without the cyano functionality. A possible mechanism for this cobalt-catalyzed carbocyclization reaction is also proposed.

Indenols, indenones and (arylcyclohexadienyl)Mn(CO)3 π-complexes from the thermally promoted reactions of alkynes with ortho-Mn(CO)4 aryl ketone, amide, ester and aldehyde derivatives

“…Later an analogous catalytic (palladium acetate) route to 1H-inden-1-ols (including 2a and 2c) directly from alkyne and o-bromoacetophenone was reported [8] for conditions very similar to those reported much earlier [9] for Pd(OAc) 2 -catalysed indenone synthesis from ortho-iodobenzaldehyde and diaryl ketones. More recently, high-yield cobalt-catalysed formation of 1H-inden-1-ols (including 2a and 2c) has been reported [10] for alkynes with o-iodoacetophenone using Co(Ph 2 PCH 2 CH 2 PPh 2 )I 2 and zinc in acetonitrile at 80°C; unsymmetrical alkynes gave similar regiochemistry patterns to those reported here.…”

“…1a (0.103 g, 0.360 mmol) and acetylene (continuous saturation) under reflux in benzene over 18 h gave Mn 2 (CO) 10 1a (0.111 g, 0.388 mmol) and 4-octyne (60 lL, 0.409 mmol) under reflux in benzene over 18 h gave Mn 2 (CO) 10 (0.009 g, 15%) and 2c (0.046 g, 51%) as colourless square plates, m.p. 79.5-81°C (lit.…”

“…1a (0.108 g, 0.378 mmol) and bis(trimethylsilyl)acetylene (0.068 g, 0.399 mmol) under reflux in benzene over 64 h gave Mn 2 (CO) 10 3.4.6. With phenylacetylene to form 1-methyl-2-phenylinden-1-ol (2f) and cyclohexadienyl complex 3a 1a (0.090 g, 0.315 mmol) and phenylacetylene (0.104 mL, 0.947 mmol) under reflux in benzene over 3.5 h gave 1-methyl-2-phenylinden-l-o1 (2f; 0.059 g, 84%) as a white solid, m.p.…”

“…Reactions of g 2 -(2-N,N-dimethylamidophenyl) tetracarbonylmanganese (1c) 3.6.1. With diphenylacetylene to form 2,3-diphenylindenone (4a) 1c (0.108 g, 0.343 mmol) and diphenylacetylene (0.062 g, 0.348 mmol) under reflux in benzene over 1 h gave Mn 2 (CO) 10 …”

Ring-closing metathesis for the synthesis of substituted indenols, indenones, indanones and indenes: Tandem RCM-dehydrogenative oxidation and RCM-formal redox isomerization

“…Recent reported methods towards the synthesis of indenols include transition metal-catalyzed carbocyclizations utilizing nickel [13], manganese [14][15][16][17], cobalt [13,18] and palladium [19][20][21][22][23], while examples of substituted indene syntheses include zirconocene- [24] and ytterbium-mediated [25], and Grignard [26] approaches. Indenones on the other hand have been synthesized by ruthenium-, [27] palladium- [28] and rhodium-mediated cyclizations [29], amongst others, as well as the treatment of suitable precursors with acids [30,31].…”