A tandem enyne/ring closing metathesis approach to 4-methylene-2-cyclohexenols: an efficient entry to otteliones and loloanolides

A short and efficient approach to a 4-methylene-2-cyclohexenone substructure present in otteliones and loloanolides is described. This strategy involves a tandem enyne/ring closing metathesis as the key reaction to construct this labile core unit.     

Synthesis of [6,n] cis-fused ring compounds via Cr-mediated dearomatisation-ring-closing metathesis

cis-Fused [6,8], [6,7], [6,6] and [6,5] ring systems containing a cyclohexadiene ring unit, a cycloenone ring and a quaternary carbon at the ring junction were obtained in only two steps from [Cr(CO)3(eta6-p-methoxyphenyl oxazoline)]. The sequence proceeds via diastereoselective addition of three C-substituents across an arene double bond, followed by allylation and ring closing metathesis (RCM). RAMP-hydrazone and (R)-isopropyloxazoline were used as chiral auxiliaries to provide, after removal of the auxiliaries, the enantiomerically highly enriched [6,7] cis-fused system.     

A tandem enyne/ring closing metathesis approach to the synthesis of novel angularly fused dioxa-triquinanes

Triquinanes and their oxygenated congeners, oxa- and dioxa-triquinanes, exhibit versatile biological activities in conjunction with synthetically challenging molecular architecture. Owing to these properties, several new strategies have been developed to accomplish the synthesis of these sesquiterpenes. Among the new strategies, cascade radical cyclization strategy has been broadly explored and well studied. Herein, we report our efforts in detail for the synthesis of dioxa-triquinanes using a domino enyne/RCM strategy as the key step. Carbohydrate based synthesis not only allows the use of inexpensive and optically pure starting materials, but also the furanose derivatives, which already possess one of the requisite dihydro-furan moieties in the desired dioxa-triquinane. The other two five-membered rings were constructed simultaneously by the cascade enyne/RCM reaction using the Grubbs' second-generation catalyst. During the course of our synthesis it was observed that the acetonide protection hinders the RCM reaction, after the initial enyne metathesis reaction. The reaction underwent smoothly under argon atmosphere, whilst use of ethylene atmosphere was found to hinder the formation of the tandem enyne/RCM product. The effect of substitution on the key reaction is described here.     

Synthetic studies on taxanes: A domino-enyne metathesis/Diels-Alder approach to the AB-ring

A domino enyne cross-metathesis/intramolecular Diels-Alder reaction has been successfully used to synthesize a bicyclo[5.3.1] undecene, corresponding to AB-ring of taxol without the gem dimethyl group.     

Aryl trihydroxyborate salts: thermally unstable species with unusual gelation abilities

A series of aryl trihydroxyborate salts were synthesized and found to form gels in benzene. The compounds were thermally unstable and readily underwent protodeboronation in solution and the solid state. Gelation could be induced without decomposition via sonication. Subsequent characterization studies revealed an unusual dependence of gel properties on alkyl chain length.     

A micromechanically motivated model for ferroelectrics combined with polygonal finite elements

Piezoelectric materials are one of the most prominent smart materials due to their strong electromechanical coupling behaviour. Ferroelectric ceramics behave like piezoelectric materials under low electrical and mechanical loads, but exhibit pronounced nonlinear response at higher loads due to microscopic domain switching. Modern smart devices consist of complex geometries that may force the ferroelectrics employed within them to experience higher fields than they were originally designed for, so that the material responds within its nonlinear region. Hence, models predicting the nonlinear effects of ferroelectrics under complex loading cases are important from the design point of view. Within standard finite element models dealing with electromechanical problems, each grain may be subdiscretized by several finite elements. This problem can be approximated or rather overcome by a polygonal finite element method, where each grain is modelled by solely one single finite element. In this contribution, a micromechanically motivated switching model for ferroelectric ceramics, as based on volume fraction concepts, is combined with polygonal finite element approach. Related representative numerical examples allow to further study and understand the nonlinear response of this material under complex loading cases. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Another form of Einstein's addition law of velocities

The velocity of a moving particle is treated in a different way. Accordingly a new form for Einstein's addition law of velocities is given. Lorentz transformations are found from this aspect. The possibility of another way of recognition of the correlation between mass and energy is explained.     

A cascade enyne/ring closing metathesis approach to angularly fused dioxatriquinanes

An expedient and first tandem enyne/ring closing metathesis approach on a sugar furanose template leading to a novel angularly fused dioxa-triquinane is described here.     

Dipolar cycloaddition of rhodium-generated carbonyl ylides with p-quinones

[reaction: see text] The dipolar cycloaddition of carbonyl ylides generated by the rhodium-catalyzed decomposition of delta- and epsilon-carbonyl-alpha-diazoketones with p-quinones leads to both C=O and C=C addition products. The product ratio is solvent- and catalyst-dependent and has been optimized to favor formation of either product. The C=C addition products of naphthoquinones are used in the assembly of structures hybridizing the illudin and anthraquinone anticancer agents.