John G. Verkade

Main group atranes: chemical and structural features

Abstract Atranes are comprised of two bridgehead atoms bridged by three three-atom moieties. When the bridgehead atoms interact, a [3.3.3.0] tricyclic system is produced; when they do not, a [3.3.3] bicyclic structure is evident. Quasi-tricyclic structures are also known in which the bridgehead-bridgehead bond length lies between the sum of the van der Waals radii and a normal transannular bond. Because of this and additional factors, atranes give rise to interesting new and useful chemistry as well as novel molecular architectures. In this review the chemical reactivities and structural properties of main group atrane systems are surveyed.

Structure-toxicity relationships of 2,6,7-trioxabicyclo[2.2.2]-octanes and related compounds☆

Abstract Many 2,6,7-trioxabicyclo[2.2.2]octanes with P, PO, PS, CH or C-alkyl substituents in the 1-position and C2H5, n-C3H7, i-C3H7, n-C4H9, or other substituents at the 4-position act at very low intraperitoneal dosages to produce convulsive seizures and death in mice. The signs of poisoning, probably resulting from stimulation of the central nervous system, resemble those of 2,6-dithia-1,3,5,7-tetrazatricyclo[3.3.1.13,7]decane-2,2,6,6-tetroxide and 1-(p-chlorophenyl)-2,8,9-trioxa-5-aza-1-silabicyclo[3.3.3]undecane, which are of similar toxicity to 4-isopropyl-1-phospha-2,6,7-trioxabicyclo[2.2.2]octane and its 1-oxide and 1-sulfide derivatives. It appears likely that toxicants of several of the chemical classes represented within the 67 compounds that were studied act at the same site in the central nervous system without having a requirement for metabolic activation. Synthesis procedures are reported here for many of these toxic materials. The findings of this study are relevant to the hazards associated with certain intermediates used in coordination chemistry and organic synthesis and with the combustion products of some flame retardants in the presence of certain polyols.

(t-Bu)2PNP(i-BuNCH2CH2)3N: New Efficient Ligand for Palladium-Catalyzed C−N Couplings of Aryl and Heteroaryl Bromides and Chlorides and for Vinyl Bromides at Room Temperature

By employing Pd(OAc)2, Cs2CO3, or NaOH, and the new ligand (t-Bu)2PN=P(i-BuNCH2CH2)3N (3a), an electronically diverse array of aryl bromides and chlorides possessing base-sensitive substituents (nitro, ester, and keto) provide coupling products with bulky aryl amines in good to excellent yields. Aryl halides possessing other functional groups including cyano, amino, trifluoromethyl, and phenol, coupled with equal ease, producing highly functionalized amines in good to excellent yields. Moreover, an aryl chloro group can be preserved in the presence of a bromo substituent under our reaction conditions. BOC-protected amines also participated efficiently. Heterocyclic bromides and chlorides underwent clean couplings with amines in excellent yields. An important strength of our protocol is the use of lower palladium loadings than those reported earlier, without compromising yields. The air-stable palladium complex (eta3-cinnamyl)PdCl.(3a) (5) was also employed successfully in C-N coupling reactions while the crotyl analogue was less efficacious. The 3a/Pd(OAc)2 catalyst system promotes, for the first time, efficient coupling of vinyl bromides with a variety of amines to produce imines and enamines at room temperature.

Pd/P(i-BuNCH2CH2)3N: an efficient catalyst for Suzuki cross-coupling of aryl bromides and chlorides with arylboronic acids

Pd(OAc)2 in combination with the commercially available ligand P(i-BuNCH2CH2)3N catalyzes the Suzuki cross-coupling reaction of a wide variety of aryl bromides and chlorides with arylboronic acids, affording the desired biaryls in excellent yields. It has also been shown that P(NMe2)3 can be employed as a ligand, though with significantly more limited success.

Enhancing Biodiesel Production from Soybean Oil using Ultrasonics

Our objective was to determine the effect of ultrasonics on biodiesel production from soybean oil. In this study, ultrasonic energy was applied in two different modes: pulse and continuous sonication. Soybean oil was mixed with methanol and a catalytic amount of sodium hydroxide, and the mixture was sonicated at threelevelsofamplitude(60, 120,and 180 μm pp ) in pulse mode (5 s on/25 s off). In the continuous mode, the same reaction mixture was sonicated at 120 μm pp for 15 s. The reaction was monitored for biodiesel yield by stopping the reaction at selected time intervals and analyzing the biodiesel content by thermogravimetric analysis (TGA). The results werecompared to a control group, in which the same reactant composition was allowed to react at 60 °C for intervals ranging from 5 min to I h without ultrasonic treatment. It was observed that ultrasonic treatment resulted in a 96% by weight isolated yield of biodiesel in less than 90 s using the pulse mode, compared to 30-45 min for the unsonicated control sample with comparable yields (83-86%). In the pulse mode, the highest yield (96%) was obtained by sonicating the mixture at 120 μm pp amplitude. In the continuous sonication mode, the highest biodiesel yield was 86% by weight, which was obtained in 15 s.

A Tetrameric Titanium Alkoxide as a Lactide Polymerization Catalyst

The tetrameric titanium alkoxide (MeC(CH 2 -μ 3 -O)(CH 2 -μ-O) 2 ) 2 Ti 4 (O-i-Pr) 10 (1) catalyzes the ring-opening polymerization (ROP) of lactide (LA) in toluene solution at various polymerization temperatures, and its bulk ROP at 130 °C. Compound 1 facilitated reasonably controlled polymerization characteristics via a coordination/insertion mechanism in solution, whereas the bulk polymerization products displayed broad molecular-weight distributions. The stereochemical microstructure of PLA was determined from homonuclear decoupled 1 H NMR spectroscopic studies.

Ligation of phosphorus ligands to silver(I). 1. Coordination of one to four P(NR2)3 ligands and the structure of a nonlinear two-coordinate complex

Etude par spectrometrie RMN de 31 P, et diffraction RX, des proprietes des liaisons des trois coordinats P (NMe 2 ) 3 , P (NMeCH 2 ) 3 CMe et P (NCH 2 CH 2 ) 3 , avec Ag (I)

Value-added oil and animal feed production from corn-ethanol stillage using the oleaginous fungus Mucor circinelloides.

This study highlights the potential of oleaginous fungus, Mucor circinelloides in adsorbing/assimilating oil and nutrients in thin stillage (TS), and producing lipid and protein-rich fungal biomass. Fungal cultivation on TS for 2 days in a 6-L airlift bioreactor, resulted in a 92% increase in oil yield from TS, and 20 g/L of fungal biomass (dry) with a lipid content of 46% (g of oil per 100g dry biomass). Reduction in suspended solids and soluble chemical oxygen demand (SCOD) in TS were 95% and 89%, respectively. The polyunsaturated fatty acids in fungal oil were 52% of total lipids. Fungal cells grown on Yeast Malt (YM) broth had a higher concentration of γ-linolenic acid (17 wt.%) than those grown on TS (1.4 wt.%). Supplementing TS with crude glycerol (10%, v/v) during the stationary growth phase led to a further 32% increase (from 46% to 61%) in cellular oil content.

P(PhCH2NCH2CH2)3N Catalysis of Mukaiyama Aldol Reactions of Aliphatic, Aromatic, and Heterocyclic Aldehydes and Trifluoromethyl Phenyl Ketone

Herein we find that proazaphosphatrane 1c is a very efficient catalyst for Mukaiyama aldol reactions of aldehydes with trimethylsilyl enolates in THF solvent. Only the activated ketone 2,2,2-trifluoroacetophenone underwent clean aldol product formation with a variety of trimethylsilyl enolates under similar conditions as the aldehydes. The reactions were carried out at room temperature using (1-methoxy-2-methyl-1-propenyloxy)trimethylsilane, whereas the temperature was -15 degrees C in the case of 1-phenyl-1-(trimethylsilyloxy)ethylene. The reaction conditions are mild and operationally simple, and a variety of aryl functional groups, such as nitro, amino, ester, chloro, trifluoromethyl, bromo, iodo, cyano, and fluoro groups, are tolerated. Product yields are generally better than or comparable to those in the literature. 1-Phenyl-1-(trimethylsilyloxy)ethylene, 1-(trimethylsilyloxy)cyclohexene, and 2-(trimethylsilyloxy)furan underwent clean conversion to beta-hydroxy carbonyl compounds under our reaction conditions. In the case of bulky (2,2-dimethyl-1-methylenepropoxy)trimethylsilane, only alpha,beta-unsaturated esters were isolated. Heterocyclic aldehydes, such as pyridine-2-carboxaldehyde, benzofuran-2-carboxaldehyde, benzothiophene-2-carboxaldehyde, and 1-methyl-2-imidazolecarboxaldehyde, gave good yields of Mukaiyama products. An optimized synthesis for the catalyst 1c is also reported herein.

INTERPLAY OF STERIC AND ELECTRONIC INFLUENCES IN THE CHEMISTRY OF MONOCYCLIC AND BICYCLIC PHOSPHORUS ESTERS

Abstract The importance of biologically active cyclic phosphorus systems has become increasingly apparent relatively recently; particularly, for example, with the discoveries of the cellular “second messenger” activities of cyclic 3′, 5′-adenosine and guanosine monophosphates and the powerful cancer therapeutic capabilities of cyclo-phosphamide and its cyclic metabolites. The earlier recognition that cyclic 2′, 3′-nucleotides formed as intermediates in the hydrolysis of polynucleotides, led to the classic researches of Westheimer and his coworkers on the hydrolysis rates of cyclic and acyclic phosphate esters.1 Within the few years the extreme toxicities of bicyclic phosphorus esters compared to their acyclic analogues have come to light2,3 along with the surprising observation that the cholinesterase inhibition of such cages is only negligible.3,4