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~~~ ~Pteridines: Synthesis and Characteristics of 5,6-Dihydro-6-( 1,2,3-trihydroxypropyl)pteridines: Covalent Intramolecular AdductsVarious 5,6-diaminopyrimidines (1, 15, 24, 33) were condensed with the phenylhydrazones of ~-( 2 ) and D-arabinoSe (3) in acidic medium under N, to give formal 5,6-dihydro-6-( 1,2,3-trihydroxypropyl)pteridines (see, e.g., 4 and 5), the latter turned out to exist prcferentially as intramolecular adducts, the hexahydropyrano-[3,2-g]pteridines 6, 7, 16, 17, 25, 26, and 34, formed subsequently by addition of the terminal OH group of the side-chain to the C(7)=N(8) bond of the pteridine moiety. Spectroscopically, the isomeric hexahydrofuro-[3,2-g]pteridines 10,11,18, 19, and 35 were also detected as minor components in the equilibrium mixtures. In the 4-amino-2-(methylthio)pteridine series, crystallization of 6 and 7 led to the stereochemically pure (3S,4R,4aR,10aS)-6-amino-3,4,4a,5,l0,l0a-hexahydro-~-(methylthio)-2~-pyrano[3,2-g]pteridine-3,4-diol (8) and its corresponding enantiomer 9, respectively. Structure 8 was proven by X-ray analysis. Acylation of the hexahydropyrano[3,2-g]pteridines yielded the more Stable tri-, tetra-, and pentaacetyl derivatives 12-14, 2&23, 27-32, and 37-39 which were characterized and of which the absolute and relative configurations were determined ('H-and I3C-NMR and UV spectra, chiroptical measurements, elemental analyses).

ions may be considered not bonded or uncoordinated. At least, their bond order is much less than one. On this basis, Rb(3) in dehydrated Rb¡ iNarA is termed zero-coordinate, zero being the sum of integers, all zero, describing its bond orders to its nearest neighbors. For this structure, the rounded-off value of 1.0 Á used in the criterion stated above may be raised to 1.5

A variety of mono-and bis[Fe(CO),(v4-diene)] complexes with alkyl, CH,OH, CHO, COCH,, COOR, and CN substituents on the 1,3-diene system have been synthesized. Dienes with a (Z)-configurated terminal Me group show steric inhibition of metal complexation resulting in lower yields and formation of tetracarbonyI($-diene) and tricarbonyl(v4-heterodiene) complexes as additional products. Regioselective attack by C-nucleophiles at the carbonyl C-atom of the functional group with or without concomitant 1,3 migration of the Fe(CO), group was used to synthesize polyenes and isoprenoid building blocks as mono-or dinuclear Fe(CO), complexes. Witfig-Homer-type reactions of Fe(CO),-complexed synthons result in stereospecific formation of (E)-configurated olefins. The 'H-, I3C-, and 57Fe-NMR spectra of 73 olefinic and allylic organoiron complexes are reported. H,H, C,H, and C,C coupling constants have been evaluated and are analyzed in tenns of the geometry of the coordinated diene. The results are corroborated by the crystal structure of tricarbonyl[3-6-q-((E)-6-methyl-3,5-heptadiene-2one)]iron (34) which shows an unusual distortion of the (CH,),C= group. The ,'Fe-NMR chemical shifts extend over the ranges of 0-600 ppm for [Fe(C0),(r14-dIene)] complexes, 7 8 N 7 10 ppm for [Fe(CO),(q'-allyl)] [BF4] and [FeX(CO),(q3-allyl)] complexes, and 1270-1690 ppm for [Fe(CO)3(q4-enone)] complexes, relative to Fe(C0)5.

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