A stereocontrolled route to a synthon for the aglycone of the aureolic acids

Cyclohexenone 3, a synthon for the aureolic acid aglycone, has been prepared using D-fucose and trimethylsilyloxybutadiene as starting materials.     

The synthesis of tricyclic naphtho[b] fused frameworks via isoquinolinium salts

The cycloaddition of the enol ethers of cyclic ketones with isoquinolinium salts is the key step in a general preparation of interesting tricyclic naphthalene derivatives.     

A Rayleigh–Ritz preconditioner for the iterative solution to large scale nonlinear problems

The approximation to the solution of large sparse symmetric linear problems arising from nonlinear systems of equations is considered. We are focusing herein on reusing information from previous processes while solving a succession of linear problems with a Conjugate Gradient algorithm. We present a new Rayleigh–Ritz preconditioner that is based on the Krylov subspaces and superconvergence properties, and consists of a suitable reuse of a given set of Ritz vectors. The relevance and the mathematical foundations of the current approach are detailed and the construction of the preconditioner is presented either for the unconstrained or the constrained problems. A corresponding practical preconditioner for iterative domain decomposition methods applied to nonlinear elasticity is addressed, and numerical validation is performed on a poorly-conditioned large-scale practical problem. This revised version was published online in June 2006 with corrections to the Cover Date.     

A novel phosphorus-carbon bond formation by ring opening with diethyl phosphite of oxazolines derived from serine

A new reaction of oxazolines derived from serine with diethyl phosphite leading to ring opening products with P-C bond formation is reported. This reaction, which proceeds under neutral conditions and without the use of any halogenated intermediate, results in a mixture of racemic α- and β-phosphono alanines in an approximate 1:2 ratio, with isolated yields up to 77%. The mechanism involves the rearrangement of the oxazoline into the corresponding α-benzamido acrylate, followed by addition of the diethyl phosphite to the double bond. Since no significant transesterification is observed, this method constitutes a simple route for α- and β-phosphono amino acids bearing suitable protecting groups.     

The face selectivity directed by an allylic group of a diene in the diels-alder reaction is reversed from that of a dienophile

The Diels-Alder reaction of 2-alkoxy hepta-3,5-dienes with N-phenyl-maleimide gives good diastereofacelectivity; and a face selectivity rule is formulated.