Rajeev S. Menon

NHC Catalyzed Transformation of Aromatic Aldehydes to Acids by Carbon Dioxide: An Unexpected Reaction†

A facile NHC-mediated reaction of aromatic aldehydes with carbon dioxide leading to carboxylic acids is described. The present protocol is mechanistically important, and it can serve as a tool for the sequestration of carbon dioxide.

Recent advances in N-heterocyclic carbene (NHC)-catalysed benzoin reactions

Summary N-Heterocyclic carbenes (NHCs) have emerged as a powerful class of organocatalysts that mediate a variety of organic transformations. The Benzoin reaction constitutes one of the earliest known carbon–carbon bond-forming reactions catalysed by NHCs. The rapid growth of NHC catalysis in general has resulted in the development of a variety of benzoin and benzoin-type reactions. An overview of such NHC-catalysed benzoin reactions is presented.

A facile three-component reaction involving [4+1] cycloaddition leading to furan annulated heterocycles

The in situ generated quinone methides from 4-hydroxycoumarin and 4-hydroxy-6-methylpyrone with various aldehydes underwent facile reaction with cyclohexyl isocyanide to produce furocoumarins in good yields. Quinone methides from 4-hydroxy-1-methylquinolinone afforded furoquinolones. The reaction presumably occurs via a [4+1] cycloaddition followed by a [1,3] H shift.

Multicomponent reactions based on nucleophilic carbenes and their applications in organic synthesis

Zwitterionic intermediates generated from the addition of nonprotic nucleophiles to activated acetylenes are intercepted with various third components constituting novel multicomponent organic transformations. Catalytic amounts of an organic base like pyridine were found to trigger reactions between an electrophilic acetylene and a variety of electrophiles. The reactions proceed through dipolar intermediates and show high stereoselectivity.

Regioselective Synthesis of Substituted Arenes via Aerobic Oxidative [3 + 3] Benzannulation Reactions of α,β-Unsaturated Aldehydes and Ketones

Facile conversion of α,β-unsaturated aldehydes and ketones into highly substituted arenes via a base-mediated, completely regioselective, air-oxidative [3 + 3] benzannulation reaction with readily available 4-sulfonylcrotonates or 1,3-bisphenylsulfonylpropene is reported. The reaction can also be carried out as a one-pot, three-component operation using 4-bromocrotonates, aryl sulfinates, and cinnamaldehyde. This open-flask, metal-free reaction does not require anhydrous solvents, proceeds under mild conditions, and uses atmospheric oxygen as the oxidant to afford high yields of the 3-(arylsulfonyl)benzoic acid esters.

Impact fragmentation of Lonar Crater, India: Implications for impact cratering processes in basalt

Impact fragmentation is an energetic process that has affected all planetary bodies. To understand its effects in basalt, we studied Lonar Crater, which is a rare terrestrial simple impact crater in basalt and analogues to kilometer-scale simple craters on Mars. The Lonar ejecta consists of basaltic fragments with sizes ranging from silt to boulder. The cumulative size and mass frequency distributions of these fragments show variation of power index for different size ranges, suggesting simple and complex fragmentation. The general shape of the fragments is compact, platy, bladed, and elongated with an average edge angle of 100°. The size distribution of cobble- to boulder-sized fragments is similar to the fracture spacing distribution in the upper crater wall, indicating the provenance of those large fragments. Its consistency with a theoretical spallation model suggests that the large fragments were ejected from near surface of the target, whereas the small fragments from deeper level. The petrophysical properties of the ejecta fragments reflect the geophysical heterogeneity in the target basalt that significantly reduced the original size of spall fragments. The presence of Fe/Mg phyllosilicates (smectites) both in the ejecta and wall indicates the role of impact in excavating the phyllosilicates from the interior of basaltic target affected by aqueous alteration. The seismic images reveal a thickness variation in the ejecta blanket, segregation of boulders, fractures, and faults in the bedrock beneath the crater rim. The fracturing, fragmentation, and fluvial degradation of Lonar Crater have important implications for Mars.

Recent shallow moonquake and impact‐triggered boulder falls on the Moon: New insights from the Schrödinger basin

Shallow moonquakes are thought to be of tectonic origin. However, the geologic structures responsible for these moonquakes are unknown. Here we report sites where moonquakes possibly occurred along young lobate scarps in the Schrodinger basin. Our analysis of Lunar Reconnaissance Orbiter and Chandrayaan-1 images revealed four lobate scarps in different parts of the Schrodinger basin. The scarps crosscut small fresh impact craters ( 1500 boulders associated with trails and bouncing marks. Their origins are largely controlled by recent impact events. Ejecta rays and secondary crater chains from a 14 km diameter impact crater traversed Schrodinger and triggered significant boulder falls about 17 Ma. Therefore, a combination of recent shallow moonquakes and impact events triggered the boulder falls in the Schrodinger basin.

[4+2] Cycloaddition reactions of o-thioquinones with pentafulvenes: efficient synthesis of benzoxathiins

o-Thioquinones undergo [4+2] cycloaddition reactions with pentafulvenes leading to 1,4-benzoxathiins. Reactions of 6-styrenylfulvene with o-thioquinones also afforded similar products.

Oxygenative and Dehydrogenative [3 + 3] Benzannulation Reactions of α,β-Unsaturated Aldehydes and γ-Phosphonyl Crotonates Mediated by Air: Regioselective Synthesis of 4-Hydroxybiaryl-2-carboxylates

Regioselective synthesis of 4-hydroxybiphenyl-2-carboxylates via the base-mediated oxygenative [3 + 3] benzannulation reaction of α,β-unsaturated aldehydes and γ-phosphonyl crotonates is reported. A hydroxyl group is installed in the final product on the originally phosphorus-bound carbon via a novel oxygenative and dehydrogenative transformation. The reaction proceeds rapidly in an open flask, uses atmospheric oxygen as an oxidant, and affords good yields of substituted biaryl phenols.

Renal sympathetic denervation for treatment of resistant hypertension – Indigenous technique

BACKGROUND The endovascular approach of ablation of renal sympathetic nerves is found to be effective in the treatment of uncontrolled hypertension. We report here our experience with the procedure in eight patients with drug resistant hypertension. METHODS We included patients in whom the blood pressure remained above 150/90 mmHg despite being on minimum three antihypertensive drugs. Radiofrequency ablation of the sympathetic nerves of both the renal arteries was done using conventional ablation catheters. The patients were followed at 1-month, 3 months and 6 months post procedure and blood pressure recorded. RESULTS All patients underwent successful renal sympathetic denervation. The mean blood pressure of the patients was 181/102.5 mmHg before the procedure and the average requirement of antihypertensive drugs per day was 4. A significant reduction in both systolic and diastolic blood pressure was observed post procedure which sustained over the follow up period of six months. The mean blood pressure observed at 1-month, 3 and 6 months were 137.5/80 mmHg, 136/81 mmHg and 137.5/81 mmHg, respectively. The average requirement of the number of antihypertensives also was reduced to 2.5 at the end of 6 months. There were no procedural complications. CONCLUSION Catheter based renal denervation causes substantial and sustained blood pressure reduction without serious adverse events in patients with resistant hypertension.