Synthesis of epoxybenzo[d]isothiazole 1,1-dioxides via a reductive-Heck, metathesis-sequestration protocol.

An atom-economical purification protocol, using solution phase processing via ring-opening metathesis polymerization (ROMP) has been developed for the synthesis of tricyclic sultams. This chromatography-free method allows for convenient isolation of reductive-Heck products and reclamation of excess starting material via sequestration involving metathesis catalysts and a catalyst-armed Si-surface.

"Click, click, cyclize": a DOS approach to sultams utilizing vinyl sulfonamide linchpins.

A diversity-oriented synthesis (DOS) strategy termed "Click, Click, Cyclize" is reported. This approach relies on functional group (FG) pairing between a vinyl sulfonamide and an array of functional groups to synthesize skeletally diverse sultams. Several FG pairing pathways on central tertiary vinyl sulfonamide linchpins have been developed including intramolecular Heck, aza-Michael, ring-closing enyne metathesis, Pauson-Khand, and chemoselective oxidation/Baylis-Hillman reactions.

α-Haloarylsulfonamides: Multiple Cyclization Pathways to Skeletally Diverse Benzofused Sultams.

The development of new methods to skeletally diverse sultams based on a central α-halo benzene sulfonamide building block is reported. Several salient features of this building block are utilized in multiple reaction pathways, including the Heck reaction, C- and O-arylation, Sonogashira-Pauson-Khand, Sonogashira-intramolecular hydroamination, lithiative cyclization and domino aza-Michael Heck for the generation of 5-, 6- and 7-membered benzofused bicyclic and tricyclic sultams.

Metathesis Cascade Strategies (ROM-RCM-CM): A DOS approach to Skeletally Diverse Sultams.

The development of a ring-opening metathesis/ring-closing metathesis/cross metathesis (ROM-RCM-CM) cascade strategy to the synthesis of a diverse collection of bi- and tricyclic sultams is reported. In this study, functionalized sultam scaffolds derived from intramolecular Diels-Alder (IMDA) reactions undergo metathesis cascades to yield a collection tricyclic sultams. Additional appendage based diversity was achieved by utilizing a variety of CM partners.

Three-component synthesis of 1,4-diazepin-5-ones and the construction of gamma-turn-like peptidomimetic libraries.

The parallel synthesis of gamma-turn-inspired peptidomimetic libraries has been demonstrated through two approaches toward the preparation of 1,4-diazepin-5-ones. In the first approach, 1,4-diazepin-5-ones scaffolds were prepared on gram scale and subsequently diversified to produce libraries. In a second approach, libraries of 1,4-diazepin-5-ones were produced directly through a three-component strategy that maximizes the diversity obtained in a single step.

New catalytic reactions of oxa- and azabicyclic alkenes.

Bicyclic alkenes, including oxa- and azabenzonorbornadienes and their derivatives, can be readily activated by transition metal complexes face-selectively due to their unsymmetrical bicyclic structure and the intrinsic angle strain on the carbon-carbon double bond. We have developed several stereo-, regio-, and chemoselective reactions catalyzed by nickel and palladium complexes using these bicyclic alkenes as substrates, providing a unique means of constructing a variety of synthetically useful carbocycles and heterocycles with high efficiency not generally accessible by traditional methods. This Account outlines these new metal-catalyzed reactions that include couplings, cycloadditions, and cyclization reactions.

Catalytic decarboxylative sp-sp3 coupling.

A palladium-catalyzed 1,4-enyne synthesis was developed based the decarboxylative coupling of acetylides with allyl electrophiles. Stereochemical studies have implicated palladium-allyl-acetylides as intermediates. Thus, decarboxylative metalation was established as an environmentally benign alternative to transmetalation from alkynyl tin reagents.

Unusual palladium-catalyzed silaboration of allenes using organic iodides as initiators: mechanism and application.

A highly regio- and stereoselective method for the synthesis of various 2-silylallylboronates 7 from allenes 1 and 2-(dimethylphenylsilanyl)-4,4,5,5-tetramethyl[1,3,2]dioxaborolane (5) catalyzed by palladium complexes and initiated by organic iodides is described. Treatment of monosubstituted aryl and alkylallenes RCH=C=CH(2) (1a-m) and 1,1-dimethylallene (1n) with borylsilane 5 in the presence of Pd(dba)(2) (5 mol %) and organic iodide 3a (10 mol %) afforded the corresponding silaboration products 7a-n in moderate to excellent yields. This catalytic silaboration is totally regioselective with the silyl group of 5adding to the central carbon and the boryl group to the unsubstituted terminal carbon of allene. Furthermore, the reactions show very high E stereoselectivity with the Z/E ratios lying in the range from 1/99 to 7/93. In the absence of an organic iodide, silaboration of 1 with 5 still proceeds, but gives products having completely different regiochemistry as that of 7. The silaboration chemistry can be applied to the synthesis of homoallylic alcohols. Treatment of allenes (1) with borylsilane 5 and aldehydes 14 in the presence of Pd(dba)(2) (5 mol %) and 3a (10 mol %) at 80 degrees C in ethyl acetate for 5 h afforded homoallylic alcohols 15a-p in one pot in good to excellent yields, with exceedingly high syn selectivity (>93%). Mechanistic pathways involving an unusual palladium-catalyzed three-component assembling reaction of dimethylphenylsilyl iodide, allene 1, and borylsilane 5 were proposed to account for these catalytic reactions.

Nickel-catalyzed addition of alkenylzirconium reagents to bicyclic olefins: a highly regio- and stereoselective ring-opening reaction.

A highly regio- and stereoselective ring-opening addition of alkenylzirconium reagents to bicyclic olefins catalyzed by nickel complexes was described. Treatment of 7-oxa- and 7-azabenzonorbornadienes (1a-e) with various terminal alkenylzirconium reagents 2a-f (Cp(2)ZrClCH=CHR; R = t-Bu, n-Pr, n-Oct, 1-cyclohexenyl, SiMe(3), and Ph) in the presence of Ni(PPh(3))(2)Cl(2) and Zn powder (or a combination of ZnCl(2) and NEt(3)) in dry THF at 50 degrees C afforded the corresponding cis-2-alkenyl-1,2-dihydronaphthalene derivatives 3a-l in moderate to excellent yields. Under similar reaction conditions, internal alkenylzirconium reagents 2g,h (Cp(2)ZrClCR=CHR: R = Et and n-Pr) also undergo ring-opening addition to oxanorbornadienes 1a and 1d to give cis-2-alkenyl-1,2-dihydronaphthalene derivatives 4a-c in good yields. Possible pathways involving the transfer of alkenyl group in the alkenylzirconium reagent to the Ni(II) center followed by migration of the alkenyl group from the Ni(II) center to the carbon-carbon double bond of 7-oxanorbornadiene or the reaction of 7-oxanorbornadiene with Ni(0) to form a Ni(II)-pi-allyl prior to the transfer of the alkenyl group as key steps for the catalytic reaction were proposed and discussed.

Cobalt-catalyzed regioselective carbocyclization reaction of o-iodophenyl ketones and aldehydes with alkynes, acrylates, and acrylonitrile: a facile route to indenols and indenes.

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.

Synthesis of phthalide derivatives using nickel-catalyzed cyclization of o-haloesters with aldehydes.

The reaction of o-bromobenzoate (1 b) with benzaldehyde (2 a) in the presence of [NiBr(2)(dppe)] (dppe=1,2-bis(diphenylphosphino)ethane) and zinc powder in THF (24 hours, reflux temperature), afforded 3-phenyl-3H-isobenzofuran-1-one (3 a) in an 86 % yield. Similarly, o-iodobenzoate reacts with 2 a to give 3 a, but in a lower yield (50 %). A series of substituted aromatic and aliphatic aldehydes (2 b, 4-MeC(6)H(4)CHO; 2 c, 4-MeOC(6)H(4)CHO; 2 d, 3-MeOC(6)H(4)CHO; 2 e, 2-MeOC(6)H(4)CHO; 2 f, 4-CNC(6)H(4)CHO; 2 g, 4-(Me)(3)CC(6)H(4)CHO; 2 h, 4-C(6)H(5)C(6)H(4)CHO; 2 i, 4-ClC(6)H(4)CHO; 2 j, 4-CF(3)C(6)H(4)CHO; 2 k, CH(3)(CH(2))(5)CHO; 2 l, CH(3)(CH(2))(2)CHO) also underwent cyclization with o-bromobenzoate (1 b) producing the corresponding phthalide derivatives in moderate to excellent yields and with high chemoselectivity. Like 1 b, methyl 2-bromo-4,5-dimethoxybenzoate (1 c) reacts with tolualdehyde (2 b) to give the corresponding substituted phthalide 3 m in a 71 % yield. The methodology can be further applied to the synthesis of six-membered lactones. The reaction of methyl 2-(2-bromophenyl)acetate (1 d) with benzaldehyde under similar reaction conditions afforded six-membered lactone 3 o in a 68 % yield. A possible catalytic mechanism for this cyclization is also proposed.

Nickel-catalyzed highly chemoselective cocyclotrimerization of arynes with allenes: a novel method for 10-methylene-9,10-dihydrophenanthrenes.

The NiBr(2)(dppe)-Zn system effectively catalyzes the [2+2+2] cocyclotrimerization of arynes with allenes, leading to 10-methylene-9,10-dihydrophenanthrenes in moderate to good yields. The cocyclotrimerization is highly selective with only the internal double bond of the allenes being involved in the reaction.

Cyclization of oxa-bicyclic alkenes with beta-iodo-(Z)-propenoates and o-iodobenzoate catalyzed by nickel complexes: a simple efficient route to annulated coumarins.

In the presence of Ni(dppe)Br(2) and Zn powder in acetonitrile at 80 degrees C, oxa-bicyclic olefins undergo cyclization with o-iodobenzoate and with beta-iodo-(Z)-propenoates to give the benzocoumarin derivatives in moderate to good yields. This methodology offers a simple efficient way for the synthesis of structurally complicate coumarins in one pot. [reaction: see text]

Cobalt-catalyzed carbocyclization of o-iodobenzaldehydes and o-iodophenylketones with alkynes.

[reaction: see text] Treatment of various o-iodobenzaldehydes and o-iodophenyl ketones with alkynes in the presence of Co(dppe)I(2) and Zn powder in acetonitrile at 80 degrees C afforded the corresponding indenols in moderate to excellent yields with exceedingly high regioselectivity. For most unsymmetrical alkynes tested, the carbocyclization gave a single regioisomer.

Nickel-catalyzed highly regio- and stereoselective three-component assembly of allenes, aryl iodides, and alkenylzirconium reagents.

Cyclohexylallene (1a) and alkenylzirconium reagent (n-PrCH=CHZr(Cp)2Cl) undergo three-component assembly with a variety of aromatic iodides (R1-I: R1 = 4-PhOMe, 4-PhCOMe, 4-PhMe, 2-thiophene, 2-PhOMe, 3-PhOMe, and 4-PhCO2Et) in the presence of NiCl2(PPh3)2 and zinc powder in THF at 50 degrees C to afford corresponding three-component assembly products in moderate to good yields with very high regio- and stereoselectivity. In addition to cyclohexylallene, also phenylallene, n-butylallene, cyclopentylallene, and cycloheptylallene underwent the three-component assembling reaction to furnish the corresponding 1,4-diene derivatives in good yields. Several alkenylzirconium reagents (R2CH=CHZr(Cp)2Cl: R2 = Ph (3b), t-Bu, TMS) were also employed for this three-component assembly. The nickel-catalyzed three-component assembly was further extended to vinyl iodides. Thus, 1a reacts with 3b and ethyl (Z)-3-iodoacrylate to produce a highly substituted triene in excellent yield. In all of these three-component assembly reactions, the E isomers were formed predominantly with E/Z ratios between 94/6 and 99/1. A possible mechanism for this highly regio- and stereoselective three-component assembly is proposed.

Regioselective synthesis of indenols via nickel-catalyzed carbocyclization reaction.

2-Halophenyl ketones 1a-e (1a, o-IC(6)H(4)COCH(3)) undergo carbocyclization with alkyl propiolates (2a, CH(3)(CH(2))(4)C[triple bond]CCO(2)CH(3); 2b, TMSC[triple bond]CCO(2)Et 2c, CH(3)C[triple bond]CCO(2)CH(3); 2d, CH(3)OCH(2)C[triple bond]CCO(2)CH(3); 2e, CH(3)(CH(2))(3)C[triple bond]CCO(2)CH(3); 2f, PhC[triple bond]CCO(2)CH(3); and 2g, (CH(3))(3)C[triple bond]CCO(2)CH(3)) in the presence of Ni(dppe)Br(2) and zinc powder in acetonitrile at 80 degrees C to afford the corresponding indenol derivatives 3a-m with remarkable regioselectivity in good to excellent yields. The nickel-catalyzed carbocyclization reaction was successfully extended to other simple disubstituted alkynes. Thus, the reaction of 2-halophenyl ketones 1a-e with disubstituted alkynes (2h, PhC[triple bond]CPh; 2i, CH(3)C(6)H(4)C[triple bond]CC(6)H(4)CH(3); 2j, CH(3)CH(2)C[triple bond]CCH(2)CH(3); 2k, PhC[triple bond]CCH(3); 2l, TMSC[triple bond]CCH(3); and 2m, PhC[triple bond]C(CH(2))(3)CH(3)) proceeded smoothly to afford the corresponding indenols 4a-t in good to excellent yields. For unsymmetrical alkynes 2k-m, the carbocyclization gave two regioisomers with regioselectivities ranging from 1:2 to 1:12 depending on the substituents on the alkyne and on the aromatic ring of halophenyl ketone. A possible mechanism for this nickel-catalyzed carbocyclization reaction is also proposed.

Asymmetric reductive ring-opening of bicyclic olefins catalyzed by palladium and nickel complexes.

[reaction: see text] Asymmetric reductive ring opening of oxa- and azabenzonorbornadienes with organic acids and zinc powder under mild conditions catalyzed by Ni(binap)Cl(2) or Pd(binap)I(2) produces the corresponding 1,2-dihydronaphth-1-ols in good to excellent yields with high enantioselectivity.

Nickel-catalyzed regioselective carbocyclization of ortho-halophenyl ketones with propiolates: an efficient route to disubstituted indenols.

Carbocylization of o-halophenyl ketones with propiolates in the presence of Ni(dppe)Br2 and Zn powder in acetonitrile at 80 degrees C afforded the corresponding 2,3-disubstituted indenols.

Highly stereoselective ring-opening addition of terminal acetylenes to bicyclic olefins catalyzed by nickel complexes.

[reaction: see text] Treatment of 7-oxa- and 7-azabenzonorbornadienes with terminal acetylenes in the presence of Ni(dppe)Cl2, ZnCl2, and Zn powder in toluene at 90 degrees C afforded the corresponding cis-2-alkynyl-1,2-dihydronaphthalene derivatives in moderate to excellent yields with remarkably high stereoselectivity.