A New Compound with C_2-Symmetry 3R,3''''R-Dihydroxy-6,6'''',6,6''''-tetramethyl-2R,2''''R,-bis-4H-pyran

InthepasttWentyyearsalargenumberofC2-syInInetryligandshavebeenreportedaschiralauxiliariesinasyInInetricsynthesis,amongwhichsomebiarylsethibitexcellentchthelselectivity."lnthispaPerwewouldreportthesynthesisofanewC2-smpetrycomPOundl,whichhastwopyranringsinsteadoftWoaromaticringsofbinyls.l,2,5-6-Diapydro-3,4-isopropylideneD-mannitol2,whichwaspreparedfromD-mannitolbyknownprocedure',wasusedasthestartingmaterialinthissynthesis.Thecarbonchainaibothterminalsofcompound2wasextendedb}'treatmentof2wi…     

Synthesis of 6,6-disubstituted penems

The synthesis of a series of 6,6-disubstituted penems starting from penicillanate 5a is described. These penems were isolated and characterized as their pivaloyloxy methyl ester.     

Photochemistry of 6,6-Dimethyl- and 2,2,6,6-Tetramethyl-2H,6H-pyran-3-one

The title compounds 1a and 1b have been synthesized in two steps from the saturated pyran-3-ones 2a and 2b , respectively. Upon irradiation (254 nm or 350 nm) in dilute solutions (10^?3?10^?2M ), compounds 1 undergo a formal [4 + 2] cycloreversion from the excited triplet state to give (2-methylprop-1-enyl)ketene ( 11 ) and either formaldehyde or acetone, ketene 11 being trapped by H₂O or MeOH to afford 4-methylpent-3-enoic acid ( 5 ) or its methyl ester 4 in 75–85% isolated yield. In this (monomolecular) photoreaction, heterocycles 1 differ from their alicyclic counterparts, i.e., 4,4-dimethylcyclohex-2-enone ( 10a ) and 4,4,6,6-tetramethylcyclohex-2-enone ( 10b ), as no rearrangement to a 4-oxabicyclo[3.1.0]hexan-2-one occurs. On the other hand, the photochemical behavior of pyranone 1a in bimolecular reactions (cyclodimerization, [2 + 2] cycloaddition to 2,3-dimethylbut-2-ene) resembles that of enone 10a .     

Polymerisation von 6,6-Dimethyltricyclo[6.4.0.02,7 dodec-3-ylmethacrylat

Ohne Zusammenfassung     

Modeling Equilibrium Behavior of Nylon 6, Nylon 6,6 and Nylon 6/6,6 Copolymer

Nylon 6 and nylon 6,6 reaction equilibria depend in a complex way on water concentration and temperature. For example, data sets from six research groups reveal that the apparent equilibrium constant for polycondensation increases with water at low water concentrations, reaches a maximum, and then decreases as the water concentration rises further. In this article, semi‐empirical expressions are proposed to describe the experimentally observed equilibrium behavior for the five main reactions that occur during nylon 6 and nylon 6,6 polymerization. Nine side reactions involving amidine ends, cyclopentanone ends, and hydrated carboxyl ends are used to develop expressions that account for the influence of both water and temperature on these equilibrium constants. Excellent fit to the data, over the entire range of the available nylon 6 and nylon 6,6 literature data, suggests that the proposed equations will be helpful for modeling reaction equilibria for nylon 6/6,6 copolymerization.     

Röntgen-struktur von 6,6-diphenylpentafulven-pentacarbonyl-diruthenium

6,6-Diphenylpentafulvenepentacarbonyldiruthenium has been synthesized and its crystal structure determined.     

The synthesis of 6,6-difluoroshikimic acid

The synthesis of 6,6-difluoroshikimic acid (4) has been achieved in nine steps from the enantiopure diol 9, which is derived from microbial dihydroxylation of iodobenzene. The synthetic strategy has also been demonstrated to be applicable to the preparation of other 6-substituted analogues of shikimic acid.     

Kristall- und molekülstruktur des bis(6,6-dimethylpentafulven)pentacarbonyl-dieisens und des 6,6-diphenylpentafulven-pentacarbonyl-dieisens

X-Ray diffraction analysis of bis(6,6-dimethylpentafulvene)pentacarbonyldiiron and 6,6-diphenylpentafulvenepentacarbonyldiiron has provided the first detailed information about the bonding in 6,6-disubstituted pentafulvenecarbonyliron complexes.