Search

Trimethylsilyl ethylene oxide has been shown to react with α-sulfonyl carbanions generated from representative primary alkyl phenyl sulfones to give the corresponding O-trimethylsilyl allylic alcohols, with higher selectivity of (Z)-isomers. The reaction proceeds by attachment of the nucleophile to the α-position of the α,β-epoxyalkylsilane followed by a carbon-to-oxygen shift to the trimethylsilyl group and expulsion of the benzenosulfonyl anion. The reaction of trimethylsilyl ethylene oxide with α,α-sulfonyl dianions followed by partial protonation of the immediate adducts affords O-trimethylsilyl allylic alcohols, mainly (E)-isomers. The reaction of trimethylsilyl ethylene oxide with α-sulfonyl carbanions generated from secondary alkyl phenyl sulfones affords α-trimethylsilyl carbinols as the only or predominant product. In this case the attachment of the nuclephile takes place at the β-position of the α,β-epoxyalkysiane. The origin of the regio- and stereo-selectivity in reactions of sulfonyl carbanions with α,β-epoxyalkylsilanes is discussed.

Anions generated from primary alkyl phenyl sulfones react with triphenylsilyloxirane to yield products of addition in the β-position, which were used for synthesis of stable cyclopropene derivatives.

The title oxidation was performed on four indolic alkaloids, β-carboline (1), reserpine (6), ajmaline (10) and ibogaine (11), leading to alicyclic hydroxylation of the starting materials. The numerous side products characterised during this reaction (due to reduction or coupling with solvent) as well as selective deuterium labelling experiments enabled us apart from the oxidation sites to study the Gif reaction mechanism

A facile, high yield synthesis of N(1), N(4)-dimethyl-5-alkyl (methyl, ethyl, n-propyl, n-butyl) cytosines has been described. This method seems to be an alternative and universal route to N(1), N(4)-methylated cytosines with any 5-substituent.

1,3-Dimethyl-5-iodouracil reacts smoothly with perfluorovinyl- (and E/Z-pentafluoropropenyl)-zinc iodides in the presence of Pd° as a catalyst yielding the appropriate 5-perfluoroalkenyl derivatives of uracil at high and moderate yield. In an analogous reaction, 1,3-dimethyl-6-iodouracils did not yield the expected coupling products.

The reduction of several indolo[2,3-a]quinolizidines with Baker's yeast (Saccharomyces cerevisiae) affords novel reduction products resulting from reduction of the indole double bond, cleavage of the C-D ring junction, or reduction of a lactam to a carbinol amine, as determined by high resolution mass spectrometry.

Syntheses of the 1α-hydroxyvitamin D 3 A ring fragment 2 from (2 R ,3 R ) 3-(triphenylsilyl)glycidol 5a and from L-(−)-malic acid are described.

Hydroxy groups on the surface of zeolite Y can be converted to phosphate groups by reaction with alkyl phosphoric acids as well as with metaphosphates when generated in the presence of the solid. Phosphonic and phosphinic acids also reacted readily with the OH groups. The products were characterized by 31P, 29Si, and 27Al NMR spectroscopy. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9: 691–698, 1998

A method for the preparation of both enantiomers of tert-butyl(methyl)phenylsilane 2 is presented. Racemic tert-butyl(methyl)phenylsilyl chloride 3 was allowed to react with (R)-(−)-2-amino-1-butanol 4 to give hydrochloride 5. Diastereomer separation via treatment of the respective free amine 6 with 0.5 mol equivalent of HCl in hexane-2-propanol yielded crystalline diastereomerically pure hydrochloride (R)Si-5. The corresponding free amine (R)Si-6 was reduced with LiAlH4 to give (S)-2. The mother liquors obtained after separation of (R)Si-5 on treatment with oxalic acid provided a crystalline salt that eventually afforded (R)-2. The optical purity of (S)-2 (98% ee) was documented by its reaction (hydrosilylation) with propargylic alcohol derivative 10 and HPLC analysis of product 11 using a chiral column.

An efficient, classical resolution of the versatile P-ligand intermediate 6-phospha-2,4,8-trioxa-adamantane (CgPH) is described and the rhodium complex of the optically pure secondary phosphine β-CgPH is an active and moderately selective asymmetric hydrogenation catalyst.

The synthesis of optically active Hagemann's esters was investigated. The starting materials in this approach were enamino esters ( R , Z )- 8 , prepared through the condensation of keto ester 6 with ( R )-1-phenylethylamine 7 . Michael addition reaction of the enamino esters ( R , Z )- 8 with methyl vinyl ketone gave the expected adducts 10 with good e.e.s of 93–96%. Subsequent annulation of the adducts furnished optically active Hagemann's esters.

The synthesis of isoquinolinone carboxylates was performed using arecoline or its isomer N-methyl tetrahydro pyridine carboxylate with Danishefsky's diene via thermal or microwave assisted Diels-Al...

A general method has been developed for the synthesis of 1,3-disubstituted-imidazo[1,5-a]quinazolin-5-(4H)-ones. This process involves initial microwave-assisted quinazolinone formation between anthranilamide and various Boc- or acylamino acids, followed by intramolecular cyclodehydration under acidic conditions. In the case of 3-monosubstituted-imidazoquinazolinones, the procedure needs the formation of the formamide derivatives by deprotection and formylation of the Boc-intermediates.

Methyl (2Z,6Z,10E,14E)- (3) and methyl (2E,6Z,10E,14E)-geranylfarnesoate (4) were prepared, and then individually cyclized in the presence of the superacid FSO3H. In the case of substrate 3, the scalaranic ester 9 (26%) and the cheilanthanic ester 10 (39%) were isolated. Under the same conditions, substrate 4 afforded a mixture of the corresponding stereoisomers 11 (25%) and 12 (63%). The observed product selectivity supports that the internal, (6Z)-configured CC bond in these and other biologically relevant substrates plays an essential role in the cyclization process.

The O-insertion reaction of a 7-phos- phanorbornene (3) unsubstituted on the double- bond gave the corresponding 2,3-oxaphosphabicyclo- [2.2.2]octene oxide (4a) in a regioselective manner that was useful in the fragmentation-related phosphonylation of alcohols. Both the UV-light mediated and the thermoinduced phosponylation accomplished on the bridged P-heterocycle (4a) were found to be sensitive toward steric factors, suggesting that beside the well-known elimination–addition reaction path taking place via metaphosphonate (11), a competitive novel addition--elimination route involving an intermediate with a pentacoordinated P-atom (12) is also present. This was confirmed by the kinetic consideration of our experimental data. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:369–375, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20213

The syntheses of imidazolo[1,5]hexopiperidinoses 2–6 and imidazol-4(5)-yl C-glycosides 7–9 are reported. The crucial step of this approach relies upon the SN2-type cyclisation of selectively protected C(1), C(2), C(3) and C(5)-substituted 1-[imidazol-4(5)-yl]pentitols in which the imidazole nitrogen or the C(1)-connected oxygen are involved as the competitive nucleophilic centers, respectively. Six selected imidazolosugars were evaluated as potential inhibitors of glycosidases.