A. V. Ignatenko

Determination of the activation parameters of permanent allylic rearrangement in allyl- and methallylboranes and in 1,1-bis(dipropylborylmethyl)ethylene by dynamic NMR spectroscopy

Abstract The activation parameters were determined for the permanent allylic rearrangement (PAR) in five organoboranes of allylic type by means of complete line shape analysis for the dynamic NMR spectra. The introduction of the second boron atom into the allylborane molecule leads to a significant decrease in the activation barrier of the PAR.

Regioselective acylation of methyl 2-methyl-4H-thieno[3,2-b]pyrrole-5-carboxylate

The influence of catalysts, acid chlorides, and solvents on the acylation of methyl 2-methyl-4H-thieno[3,2-b]pyrrole-5-carboxylate was studied. The use of AlCl3 allows the regioselective introduction of the acyl group into position 3 to be performed, whereas the acyl group is regioselectively introduced into position 6 of thienopyrrole when SnCl4 is used.

Reductive allylation of pyrrole with allylboranes. Synthesis oftrans- andcis-2,5-disubstituted pyrrolidines

Pyrrole undergoes reductive mono- and diallylation on successive treatment with β,γ-unsaturated organoboron derivatives (triallylborane, allyl(dipropyl)borane, and triprenylborane) and alcohols to give 2-allylated 3-pyrrolines andtrans-2,5-diallylated pyrrolidines. The addition of both the first and second boron-allylic fragment to the heterocycle proceeds with rearrangement. A method for transformation of thetrans-2,5-diallylpyrrolidine into thecis-isomer (heating with triallylborane at 190 °C) was developed and a series ofN-substituted derivatives of these pyrrolidines was synthesized. A method for the preparative synthesis of nonsymmetrically substitutedtrans- andcis-2-alkyl(phenyl)-5-allylpyrrolidines, based on reductive allylboration of pyrrole followed by 1,2-addition of RLi to the 5-allyl-1-pyrroline that formed, was also developed. A direct confirmation of intermediate formation of 2H- and 3H-pyrrole tautomers under the action of allylboranes was obtained. The adduct of 2H-pyrrole with BF3 was detected by NMR spectroscopy.

Preparation oftrans- andcis-2-allyl-6-alkyl(aryl)-1,2,3,6-tetrahydropyridines based on the reductivetrans-2,6-dialkylation of pyridine. Synthesis of (±)-epidihydropinidine and (±)-dihydropinidine

A general method for the preparation of unsymmetricaltrans-2-allyl-6-alkyl(aryl)-1,2,3,6-tetrahydropyridines6 based on a combination of 1,2-addition of RLi to pyridine andtrans-6-allylation with triallylborane in the presence of methanol was elaborated. It was shown thattrans-piperideines (6 (R=Alk, Ph) isomerize into the correspondingcis-2-allyl-6-alkyl(phenyl)-3-piperideines14 on heating with triallylborane followed by deboronation of aminoborane (16) with methanol and an alkali. The stereochemistry of compounds6 and14 was determined by two-dimensional NOE spectroscopy. A possible mechanism of the formation oftrans-amines6 and their transformation intocis-isomers14 is discussed. Alkaloids (±)-epidihydropinidine (trans-2-methyl-6-propylpiperidine2a, 70%) and (±)-dihydropinidine (cis-2-methyl-6-propylpiperidine1d, 71%) were synthesized by hydrogenation of compound6a (R=Me) and14a (R=Me), respectively, over Raney nickel.

Reductivetrans-2,6-diallylation of pyridines with allylboranes. Synthesis oftrans- andcis-2,6-diallyl-1,2,5,6-tetrahydropyridines and their deuterated derivatives

The reductivetrans-2,6-diallylation of pyridines with triallyl- and allyl(dialkyl)boranes has been discovered. Heating (40–100 °C) of pyridine, deuteropyridine, or 3-bromopyridine complexes with triallylborane in the presence of alcohols (ROH or CH3OD), water, or Et2NH results in the respectivetrans-2,6-diaIlyl-1,2,5,6-tetrahydropyridines (2,3,22, or25) in 20–97 % yields. A preparative method for the isomerization oftrans-2,6-diallyl compounds2 and25 into the respectivecis-isomers4 and28 by heating them with triallyl- or allyl(dialkyl)boranes (125–150 °C) has been suggested. The hydrogenation oftrans- orcis-2,6-diallyl-1,2,5,6-tetrahydropyridines gavetrans- orcis-2,6-dipropylpiperidines, respectively. Thecis- andtrans-configurations of compounds2 and4 were established by analyzing the NMR spectra ofN-benzyl (7 and13) andN,N-dimethyl (6 and 14) derivatives of piperidine derivatives5 and8. A possible mechanism for the reductive diallylation of pyridines has been discussed.

Preparation of 1-substituted 1-vinylcycloalkanes from 3,3-tetra- and 3,3-penta-methyleneallylboranes

Abstract The boranes I and II, obtained by hydroboration of 1,1-tetra- and 1,1-pentamethyleneallenes with 9-BBN, were used as key reactants in the synthesis of a series of unsaturated gem -substituted carbinols (VIIa-VIIg, Xa-Xc, and XII), as well as 1,1-divinylcyclopentane and 1,1-divinylcyclohexane (XV and XVIII). The addition reactions of the boranes I and II to the carbonyl compounds and ethoxyacetylene studied, and the protolytic cleavage of II occur with total rearrangement of the allylic moiety.

Transformations of pyridine and deuteropyridine under the action of trimethallylborane and alcohols. Synthesis oftrans- andcis-2,6-dimethallyl-1,2,3,6-tetrahydropyridines and theirN-derivatives

Reductivetrans-2,6-dimethallylation of pyridine and deuteropyridine with trimethallylborane in the presence of alcohols proceeds at room temperature,i.e., under substantially milder conditions than the analogous reaction with the participation of triallylborane.trans-2,6-Di(2-methylallyl)-1,2,3,6-tetrahydropyridine (3) was obtained in a yield of 87%. When heated with trimethallylborane (130–135°C, 2.5 h), compound3 underwent isomerization tocis-2,6-di(2-methylallyl)-1,2,3,6-tetrahydropyridine (4). Hydrogenation oftrans- (3) andcis-isomers (4) yieldedtrans- andcis-2,6-diisobutylpiperidines, respectively. The heterocycles obtained wereN-functionalized by reactions with MeI, PhCH2Cl, ethylene oxide, and perfluoropropyloxirane. The stereochemistry of thecis- andtrans-isomers (3 and4) was established based on the NMR spectra of theirN,N-dimethyl salts and the products of the reaction with ethylene oxide.trans-2,6-Dimethallyl-2,3,4,5,6-pentadeutero-1,2,3,6-tetrahydropyridine and a number of its derivatives were prepared from the complex of trimethallylborane with C5D5N. A probable mechanism of the reductivetrans-2,6-diallylation of pyridines with allylboranes in the presence of alcohols is discussed.

Addition of thiols to ethyl 4,4,4-trifluorocrotonate

Ethyl 4,4,4-trifluorocrotonate 1 readily adds aliphatic and aromatic thiols and aminothiols at the double bond in the presence of catalytic amounts of alkylamines and ammonia to give 3-thiolation products. Thiolacetic acid reacts with ester 1 in the absence of a catalyst at 100 °C.

Stereoselective synthesis of (+)-indolizidines 167B and 209D and their trans-isomers based on the reductive allylboration of pyridine

A general method for the synthesis of 5-substituted indolizidines based on intramolecular cyclization oftrans- andcis-2-allyl-6-R-1,2,3,6-tetrahydropyridines, obtained from pyridine and triallylborane, has been elaborated. The closure of the five-membered ring is carried out by hydroboration-oxidation followed by cyclization of the resulting δ-amino alcohols in the presence of the Ph3P−CBr4−Et3N system. (Pr2BH)2 and Pr3B are used as the hydroborating reagents, and H2O2 in an acid medium is used for the oxidation of 2-[3-(dipropylboryl]-Δ2-piperideines formed. This method has been used for the synthesis of two natural alkaloids: indolizidine 209D (cis-5-hexylindolizidine) and itstrans-isomer were prepared fromcis- andtrans-2-allyl-6-hexyl-1,2,3,6-tetrahydropiridine, respectively; indolizidine 167B andtrans-5-propylindolizidine were synthesized fromcis- andtrans-2,6-diallyl-1,2,3,6-tetra-hydropyridine, respectively.

Synthesis of functional derivatives of 2-methylenecyclopentane and 2-methylenecyclohexane based on the allylborylation of imines, nitriles, isocyanates, and isothiocyanates by cycloalkenylmethyl(dipropyl)boranes

A study has been made of the allylborylation of imines, nitriles, isocyanates, and isothiocyanates by the action of cycloalkenylmethyl(dipropyl)boranes. Preparative methods have been developed for obtaining amines, phenylamides, and phenylthioamides of the 2-methylenecyclopentane and 2-methylenecyclohexane series.