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International audience; Heteroarylsilyl cations elaborated from a quinoline skeleton have been prepared from the corresponding silanes and their structures studied by 1 H, 29 Si, and 15 N NMR. DOSY experiments and DFT calculations were also carried out showing that the silyl cation center is stabilized intramolecularly by the quinoline nitrogen atom (N1), forming a highly strained and quasi planar 4-membered ring. Oxygenated and nitrogenated substituents at the C4 position on the quinoline ring were shown to reinforce the Si-N1 interaction through a p- conjugation. The Lewis acidity of this class of silylium was finally determined using Müller's nitrilium method.

The use of gem-diborylalkenes as radical-reactive groups is explored for the first time. These reactions provide an efficient and general method for the photochemical conversion of gem-diborylalkenes to rapidly access 1,1-bisborylalkanes. This method exploits a novel photoredox decarboxylative radical addition to gem-diborylalkenes to afford α-gem-diboryl carbon-centered radicals, which benefit from additional stability by virtue of an interaction with the empty p-orbitals on borons. The reaction offers a highly modular and regioselective approach to γ-amino gem-diborylalkanes. Furthermore, EPR spectroscopy and DFT calculations have provided insight into the radical mechanism underlying the photochemistry reaction and the stability of the bis-metalated radicals, respectively.

Organoborons are extremely important for synthetic organic chemistry; they can serve as advanced intermediates for a variety of transformations. Such a well-known transformation involves the loss of the boron moiety, creating alkyl radicals. Although these originally developed protocols for alkyl radical generation remain in active use today, in recent years their α-boryl carbon-centred radicals have been joined by a new array of radical generation strategies that offer a unique reactivity to forge a wider diversity of organoborons that often operate under mild and benign conditions. Herein, we will highlight the stability and reactivity of α-borylalkyl radicals and their remarkably recent advances in order to further utilise them for C-C and C-heteroatom bond formation. Their use for this purpose has been reported over the last decade in an attempt to guide the synthetic community. Various transition-metal and metal-free methods for their generation are presented, and more advanced photoredox approaches are discussed, mainly for the period of 2009-2019.

An efficient and general method for the chemoselective synthesis of unsymmetrical gem-diborylalkanes is reported. This method is based on a late-stage desymmetrization through nucleophilic "trifluorination", providing chiral gem-diborylalkanes bearing a trifluoroborate group. The reaction offers a highly modular and diastereoselective approach towards the synthesis of gem-diborylcyclopropanes. The utility of the gem-diborylalkane building blocks was demonstrated by selective post-functionalization of the trifluoroborate group. These functionalizations include inter- and intra- Pd-catalyzed Suzuki-Miyaura coupling reactions.

Department of Chemistry, Indian Institute of Science Education and Research Bhopal, Bhauri, Bhopal-462 066, Madhya Pradesh, India Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur-741 246, Nadia, West Bengal, India E-mail: alakesh@iiserkol.ac.in Manuscript received online 14 November 2020, revised and accepted 20 December 2020 An expedient synthesis of fluorinated 2-oxindoles bearing an all carbon quaternary center at the pseudobenzylic position is envisioned under “transition metal free” intramolecular dehydrogenative coupling (IDC) pathway. This method has been applied to a wide range of substrate affording fluorinated 2-oxindoles in moderate to good yields in a facile one-pot C-alkylation concomitant with oxidative coupling strategy. There are several advantages of our methodology, namely, (i) transition metalfree process and simple oxidants are used and (ii) wide substrate scope. The control experiment using radical scavenger suggesting that reaction goes via radical pathway. Further works on the biological potential of these fluorinated 2-oxindoles are currently under active investigation.

A new efficient strategy to access benzylic carbamates through C-H activation is reported. The use of a catalytic amount of a Cu(i)/diimine ligand in combination with NFSI ((PhSO2)2NF) or F-TEDA-PF6 as oxidants and H2NCO2R as an amine source directly leads to the C-N bond formation at the benzylic position. The mild reaction conditions and the broad substrate scope make this transformation a useful method for the late-stage incorporation of a ubiquitous carbamate fragment onto hydrocarbons.

Today’s developmental world needs large amount of energy. Due to the limited fossil fuel source, there is need of some alternate fuel sources among which biodiesel from vegetable oil widely practiced. There is an increasing interest in India to search for suitable low cost alternative fuels that are Eco friendly. Biodiesel is a renewable, biodegradable and non toxic fuel. In this paper an attempt has been made to study and compare the oil percentage and Fatty acid methyl ester (FAME) components of three non edible oil seed plants abundantly found in Bihar, India. Oil from the seed kernel was extracted by solvent extraction technique through Soxhlet apparatus using n-hexane as solvent. Percentage oil content for Jetropha, Mahua and Castor are found around 76 %, 41% and 33% respectively. Further extracted oil were analysed by GC-MS for their FAME components. Palmitic, linoleic, oleic are most common fatty acid found among three.

We report an efficient Pd(0)-catalyzed deacylative allylation of N-acyl 3-substituted 2-oxindoles via the coupling of in situ generated nucleophiles (3 and 4) with allyl electrophiles for the synthesis of a variety of 2-oxindoles with C3-quaternary centers. Gratifyingly, this alkylation process is found to be highly chemoselective in nature, where a C-C bond formation is completely predominant over a C-N bond formation. A variety of key intermediates were synthesized utilizing an aforementioned methodology.

A general strategy for asymmetric approach to the hexahydropyrrolo[2,3-b]indole alkaloids sharing a vicinal quaternary-tertiary centers has been disclosed via Pd(0)-catalyzed N-deacylative allylations (N-DaA) (dr > 20:1). Utilizing this strategy, asymmetric total syntheses of pseudophrynamines 270 (3c) and 272A (3b) have been achieved from a 3-substituted N-acyl indole 8 (pro-nucleophile) with allyl alcohol (pro-electrophile).

International audience; A new efficient strategy to access benzylic carbamates through C-H activation is reported. The use of a catalytic amount of Cu(I)/diimine ligand in combination with NFSI ((PhSO2)2NF) or F-TEDA-PF6 as oxidants and H2NCO2R as an amine source, direct leads to the C-N bond formation at benzylic position. The mild reaction conditions, and broad substrate scope make this transformation a useful method for a late-stage incorporation of the ibiquitous carbamate fragment onto hydrocarbons.

The use of gem-bis-metalated-alkenes, i.e., vinyl gemdiboron-compound, as light-labile substrates is explored for the first time. The knowledge gained provided us with an in-depth understanding of the reactivity of novel radical intermediates of geminal-metalated ethane. This methodology can serve as the late-stage diversification of bioactive molecules and simple organic molecules in which it drives the synthesis of gemdiborylalkanes.

FeCl3-catalyzed cyclization of an arylvinyl carbinols has been explored for efficient synthesis of [6,5,6]-carbotricyclic core of taiwaniaquinoids sharing an all-carbon quaternary center at the pseudobenzylic position. The methodology works under mild conditions, in an open flask, to afford key carbotricyclic core in excellent yields. The strategy has been applied to a concise synthesis of naturally occurring taiwaniaquinoids, (±)-dichroanal B (1 h) in 10 steps from β-cyclocitral 7 in 34.7 % overall yield.

The synthesis of a variety of 2-oxindoles bearing an all-carbon quaternary center at the pseudo benzylic position has been achieved via a ‘transition-metal-free’ intramolecular dehydrogenative coupling (IDC). The construction of 2-oxindole moieties was carried out through formation of carbon–carbon bonds using KOt-Bu-catalyzed one pot C-alkylation of β-N-arylamido esters with alkyl halides followed by a dehydrogenative coupling. Experimental evidences indicated toward a radical-mediated path for this reaction.

A versatile unprecedented strategy to diversely functionalized hexahydropyrrolo[2,3-b]indole alkaloids is described in high chemical yields. The synthesis features a key Pd(0)-catalyzed deacylative alkylation of N-acyl 3-substituted indoles using only 1 mol% of Pd(PPh3)4. The scope of this methodology is further defined in the asymmetric synthesis of pyrroloindolines using a diastereoselective approach.

An expeditious approach to catalytic enantioselective total syntheses of crinine-type Amaryllidaceae alkaloids has been accomplished via a Pd-catalyzed enantioselective decarboxylative allylation of allylenol carbonates as a key step (up to 96% ee). Using this strategy, collective total syntheses of Amaryllidaceae alkaloids such as (-)- epi-elwesine (1b), (-)-crinine (1c), (-)- epi-crinine (1e), (-)-oxocrinine (1f), and (-)-buphanisine (1d) have been accomplished. Gratifyingly, naturally occurring Amaryllidaceae alkaloids such as (+)-vittatine (1g), (+)- epi-vittatine (1h), and (+)- epi-elwesine (1i) [enantiomers of (-)-1c, (-)-1e, and (-)-1b, respectively] have also been achieved by switching the antipode of ligand used in the catalytic enantioselective step.

We present an effective deacylative alkylation strategy for the construction of a variety of 2-oxindoles bearing an all-carbon quaternary center at the pseudobenzylic position. A wide variety of products with quaternary centers could be accessed by employing simple Pd(0) catalysis under mild reaction conditions. Importantly, the same strategy works equally well for the dimeric 2-oxindole system, furnishing products with a vicinal quaternary center in favour of meso-isomer as the major product. Eventual application to the total syntheses of meso-chimonanthine and meso-folicanthine very well demonstrates the synthetic potential of this strategy.

A Lewis acid catalyzed Nazarov-type cyclization of arylvinylcarbinol has been developed for the asymmetric synthesis of carbotetracyclic core of merosesquiterpenes. The reaction works only in the presence of 2 mol % of Sn(OTf)2 and Bi(OTf)3 in dichloroethane under elevated temperature. The methodology offers the synthesis of a variety of enantioenriched arylvinylcarbinols from commercially available (3aR)-sclareolide 9 in six steps with an eventual concise total synthesis of marine sesquiterpene quinol, akaol A (1a).

A Lewis acid catalyzed Nazarov-type cyclization of arylvinylcarbinol has been developed for the asymmetric synthesis of carbotetracyclic core of merosesquiterpenes. The reaction works only in the presence of 2 mol % of Sn(OTf)2 and Bi(OTf)3 in dichloroethane under elevated temperature. The methodology offers the synthesis of a variety of enantioenriched arylvinylcarbinols from commercially available (3aR)-sclareolide 9 in six steps with an eventual concise total synthesis of marine sesquiterpene quinol, akaol A (1a).