Generation and Reactions of sp2-Carbanionic Centers in the Vicinity of Heterocyclic Nitrogen Atoms

Acyl-Directed ortho-Borylation of Anilines and C7 Borylation of Indoles using just BBr3

Indoles are privileged heterocycles found in many biologically active pharmaceuticals and natural products. However, the selective functionalization of the benzenoid moiety in indoles in preference to the more reactive pyrrolic unit is a significant challenge. Herein we report that N-acyl directing groups enable the C7-selective C-H borylation of indoles using just BBr3 . This transformation shows some functional-group tolerance and notably proceeds with C6 substituted indoles. The directing group can be readily removed in situ and the products isolated as the pinacol boronate esters. Acyl-directed electrophilic borylation can be extended to carbazoles and anilines with excellent ortho selectivity. 4-amino-indoles are amenable to this process, with acyl group installation and directed electrophilic C-H borylation enabling selective formation of C5-BPin-indoles.

Chichibabin-type direct alkylation of pyridyl alcohols with alkyl lithium reagents

Direct C(6) alkylation of pyridyl alcohols can be achieved following an initial deprotonation of the hydroxy group. This transformation, which is believed to occur by a Chichibabin-type alkylation, avoids lateral deprotonation prior to pyridine ring alkylation and gives increased regioselectivity for C(6) over C(4) alkylation.

A facile, mild and efficient one-pot synthesis of 2-substituted indole derivatives catalyzed by Pd(PPh3)2Cl2

2-Phenylindoles were prepared by heteroannulation of 2-haloaniline derivatives and phenylacetylene under mild conditions in a one-pot reaction catalyzed by Pd(PPh3)2Cl2.

Gas-phase acidity studies of multiple sites of adenine and adenine derivatives

The acidities of multiple sites in the purine nucleobase adenine (1) and adenine alkyl derivatives 9-ethyladenine (2), 3-methyladenine (3), 1-methyladenine (4), and N,N-dimethyladenine (5) have been investigated for the first time, using computational and experimental methods to provide an understanding of adenine reactivity. We have previously measured two acidic sites on adenine, with the N9 site being 19 kcal mol(-)(1) more acidic than the N10 site (333 +/- 2 versus 352 +/- 4 kcal mol(-)(1), respectively). In this work, we have established that 9-ethyladenine has two sites more acidic than water: the N10 (352 +/- 4 kcal mol(-)(1)) and the C8 (374 +/- 2 kcal mol(-)(1)). We have likewise measured two acidities for 3-methyladenine, the N10 (347 +/- 4 kcal mol(-)(1)) and the C2 (370 +/- 3 kcal mol(-)(1)). For 1-methyladenine and N,N-dimethyladenine, we measure the N9H acidity to be 331 +/- 2 and 333 +/- 2 kcal mol(-)(1), respectively. We believe that the bracketing of only one site for the latter species is a kinetic effect, which we discuss further in the paper. Computationally, we have found the interesting result that some of the vinylic C-H sites in these purine bases are predicted to be much more acidic than water (DeltaH(acid) = 390.7 kcal mol(-)(1)) in the gas phase, on the order of 373 kcal mol(-)(1). The acidic vinylic C-H sites are always adjacent to an N-R group, and this pattern is maintained regardless of whether the site is on the five- or six-membered ring of the purine. Vinylic C-H sites elsewhere on the purine have calculated acidities of about 400 kcal mol(-)(1). The differing acidities are interpreted through electrostatic potential calculations. We also relate our results to the intriguing biochemical decarboxylation of orotate ribose monophosphate, which involves a vinylic anion adjacent to an N-R group; this decarboxylation is the last step in the de novo biosynthesis of pyrimidine nucleotides, and the enzyme that catalyzes the reaction, orotate ribose monophosphate decarboxylase, has been the subject of intense study recently, as its mechanism remains elusive.

Addition of Indolyl and Pyrrolyl Grignard Reagents to 1-Acylpyridinium Salts

Certain indolyl and pyrrolyl Grignard reagents add to 1-acyl salts of 4-methoxy-3-(triisopropylsilyl)pyridine to give the corresponding 1-acyl-2-heteroaryl-2,3-dihydro-4-pyridones in good to high yield. When the 1-acyl group contained a chiral auxiliary, (+/-)-trans-2-(alpha-cumyl)cyclohexyloxy, addition of the indolyl Grignards resulted in a separable mixture of diastereomeric 2,3-dihydro-4-pyridones.

Regioselective Sonogashira couplings of 2,4-dibromoquinolines. A correction

Heteronuclear multiple bond correlation (HMBC) was used to determine the regiochemical outcome of palladium-catalyzed carbon-carbon bond formation between 2,4-dibromoquinolines and terminal acetylenes. The observed regioselectivity of these coupling reactions is opposite to that reported in the literature for analogous reactions.

Benzotriazole- and 1,2,4-Triazole-Stabilized Allylic Anions: Applications in Syntheses of Functionalized alpha,beta-Unsaturated Ketones, gamma-Lactones, gamma-Lactams, and beta-Substituted Esters

Deprotonated 1-(benzotriazol-1-yl)-1-ethoxy-2-hexene (7) reacted with alkyl halides, aldehydes, ketones, imines, and alpha,beta-unsaturated esters to give exclusively the alpha-alkylated products 8a-c, 10a,b, 12, 14, 16, and 18a,b, respectively. Without isolation, these products were hydrolyzed under mild conditions to generate the corresponding simple or functionalized alpha,beta-unsaturated ketones 9a-c, 11a,b, 13, 15, 17, and 19a,b. Similar reactions with the phenyl-substituted analog 3-(benzotriazol-1-yl)-3-ethoxy-1-phenyl-1-propene (21) also gave the analogous alpha-products, but they were accompanied by small amount of the gamma-products in most cases. By contrast, deprotonation of the corresponding triazole derivative 29 with butyllithium followed by reactions with alkyl halides, aldehydes, ketones, or imines yielded exclusively gamma-alkylated adducts 32, 34, 36, 38, 40, and 42. Intermediates 32, 34, 36, 38, 40, and 42 were readily converted into beta-substituted esters 33a-c, gamma-lactones 35a,b, 39, 41, and 43, and gamma-lactams 37a-c on hydrolysis.

Novel Syntheses of alpha,beta-Unsaturated Esters, alpha,beta-Unsaturated gamma-Lactones, and 2-Alkoxypyrroles via 1,2,4-Triazole-Stabilized Allenic Anions

The dianion 12 (right harpoon over left harpoon 13) of 1-(1,2,4-triazol-1-yl)phenylpropargyl ethyl ether 11(readily prepared from phenylpropargylaldehyde diethyl acetal 8 and 1,2,4-triazole) reacts with alkyl halides, aldehydes, ketones, and alpha,beta-unsaturated ketones to give exclusively gamma-substituted allenic products of type 10. These adducts underwent mild in situ hydrolysis enabling convenient syntheses of alpha,beta-unsaturated esters 9a-c and alpha,beta-unsaturated gamma-lactones 16, 18, 20, and 22. Reactions of dianion 13 with imines generated the 1,3,4-trisubstituted 2-alkoxypyrroles 27, 30, and 31 in high yields. The alkyl-substituted analog 34 underwent similar reactions to give predominantly the gamma-products 39,40, and 42 along with a small proportion of alpha-analogs.