Oxazolium-derived azomethine ylides. External oxazole activation and internal dipole trapping in the synthesis of an aziridinomitosene

Intermolecular alkylation of the aziridinyl oxazole 20 using PhSO(2)CH(2)CH(2)OTf is possible despite the presence of potentially nucleophilic aziridine nitrogen. The resulting oxazolium salt 22 reacts with BnNMe(3)(+)CN(-) to produce the azomethine ylide 24b via electrocyclic ring opening of an oxazoline 23b. Internal cycloaddition affords 26 in 66% yield. After saponification and base-induced cleavage of the N-phenylsulfonylethyl group, conventional cyclization provides access to 33. Deprotection and DDQ oxidation completes the synthesis of the aziridinomitosene derivative 9b. The starting cis-disubstituted aziridine ester 16 can be prepared by the aza-Darzens reaction of 15 with tert-butyl chloroacetate.     

On the simultaneous measurement of position and momentum: Naimark embeddings and projections

Single and double meter simultaneous measurements of a harmonic oscillator are reviewed and compared. Naimark extensions are constructed and relevant projection properties are exhibited for both cases. The theory is extended to the simultaneous measurement of squeezed position and momentum measurements.     

Practical asymmetric synthesis of alpha-branched 2-piperazinylbenzylamines by 1,2-additions of organometallic reagents to N-tert-butanesulfinyl imines

[reaction: see text] 2-[4-(tert-Butoxycarbonyl)piperazinyl]benzylidene-tert-butanesulfinamides underwent nucleophilic 1,2-addition with different organometallic reagents to give highly diastereomerically enriched adducts. X-ray crystallography of the resulting alpha-branched N-Boc-2-piperazinylbenzyl-tert-butanesulfinamides confirms different mechanisms depending on the organometallic reagent used. Differential deprotection of the N-Boc and the tert-butanesulfinamides was investigated, and the dehydration byproducts have been identified and characterized. To avoid the formation of byproducts in the acidic deprotection step, the N-tert-butanesulfinamide group was converted to the corresponding N-tert-butanesulfonamide (Bus), which allowed for clean orthogonal deprotection. The efficient synthesis and deprotection of the N-Boc-2-piperazinylbenzyl-tert-butanesulfinamides herein described constitutes an attractive method for extensive structure-activity studies in the search for novel ligands of the human melanocortin 4 receptor.     

Adjoint Clifford Rings

Let > be a ring and define , which yields a monoid , called the {\it adjoint semigroup\/} or {\it circle semigroup\/} of . This paper continues the authors" investigations into the relationship between a ring and its adjoint semigroup, focusing here on the case where is a Clifford semigroup. Such rings are called {\it adjoint Clifford rings.\/} Structure theory for such rings is developed and examples are given to illustrate and delimit the theory.     

Velcrands with snaps and their conformational control

A novel class of self-folding velcrands was prepared that dimerize through intermolecular forces. Solvophobic interactions on extended pi surfaces stabilize the dimer similar to velcrands, while eight hydrogen bonds act like snaps to hold the molecules together. The self-complementary array of hydrogen bonding sites were incorporated on the upper rim of a resorcinarene-based cavitand. A dramatic reorganization of shape and size of the internal cavity was manifested through changes in solvent polarity. Specifically, the equilibrium between the extended surface (D2d symmetry) and a deep cavity (C4v symmetry) could be manipulated in mixtures of aromatic solvents (or CDCl3) and [D6]DMSO. The switching of conformations and the dimerization motif are well-suited for the assembly of noncovalent polymeric materials.     

Stereocontrolled synthesis of (-)-macrolactin A

The total synthesis of (-)-macrolactin A, a 24-membered macrolide, has been achieved using a newly developed 1,3-diol synthon for the introduction of two key stereogenic centers. The synthon was derived from sequential use of the Noyori asymmetric reduction followed by chiral sulfoxide methodology. Tellurium-derived cuprate organometallics offered an efficient and highly stereoselective means for installation of the C8 Z/E-diene, while the C15 E/E-segment was derived from a Julia-Lythgoe olefination. Yamaguchi lactonization was used to secure the macrocycle in a convergent approach with the longest linear sequence of 19 steps from Noyori alcohol 6.