Oxetanes from the Ring Contraction of ?-Triflates of ?-Lactones: Oxetane Nucleosides and Oxetane Amino Acids

?-Triflates of ?-lactones with potassium carbonate in methanol give efficient contraction of the ring to oxetane-1-carboxylates in which the oxygen substituent at C(3) of the oxetane is predominantly trans to the carboxylate at C(2), regardless of the stereochemistry of the starting triflate. The limitations of the procedure are discussed and compared with analogous reactions for the preparation of THF carboxylates. The potential of the contraction in the preparation of oxetane nucleosides (such as oxetanocin) and oxetane sugar amino acids (analogues of oxetin) as peptidomimetics with predisposition to form secondary structural motifs is illustrated

2-De­oxy-2,3-O-isopropyl­idene-2,4-di-C-methyl-β-l-arabinose

X-ray crystallography unequivocally confirmed the stereochemistry of the C atom at position 2 in the carbon scaffold of the title mol­ecule, C10H18O4. The pyran­ose ring exists in a chair conformation with the methyl group on the C atom in the 2 position in an equatorial configuration. The absolute stereochemistry was determined from the starting material. The crystal structure consists of O—H⋯O hydrogen-bonded chains of mol­ecules running parallel to the b axis

2,3-O-(S)-Benzyl­idene-2-C-methyl-d-ribono-1,4-lactone

The crystal structure of the title compound, C13H14O5, establishes (i) the (S) – rather than (R) – configuration at the acetal carbon and (ii) that both the acetal and the lactone form five- rather than six-membered rings; the absolute configuration is determined by the use of 2-C-methyl-d-ribono-1,4-lactone as the starting material. The compound consists of hydrogen-bonded chains of mol­ecules running along the a axis; there are no unusual packing features. Only classical hydrogen bonding has been considered

(4R)-4-(2-Allyl-2H-1,2,3-triazol-4-yl)-1,2-O-isopropyl­idene-l-threose

X-ray crystallography unequivocally confirmed the structure of the title compound, C12H17N3O4, as (4R)-4-(2-allyl-2H-1,2,3-triazol-4-yl)-1,2-O-isopropyl­idene-l-threose. The absolute configuration was determined by the use of d-glucorono-3,6-lactone as the starting material. The crystal structure consists of hydrogen-bonded chains of mol­ecules running parallel to the a axis. There are no unusual packing features

tert-Butyl 2-de­oxy-4,5-O-isopropyl­idene-d-gluconate

The relative configuration of tert-butyl 2-de­oxy-4,5-O-iso­propyl­idene-d-gluconate, C13H24O6, an inter­mediate in the synthesis of 2-de­oxy sugars, was determined by X-ray crystallography, and the crystal structure consists of chains of O—H⋯O hydrogen-bonded mol­ecules running parallel to the a axis. There are two mol­ecules in the asymmetric unit. The absolute configuration was inferred from the use of d-erythrono­lactone as the starting material

(4S,5R,6R)-Methyl 4-hydr­oxy-4,5-iso­propyl­idenedioxy-4,5,6,7-tetra­hydro-1,2,3-triazolo[1,5-a]pyridine-3-carboxyl­ate. Erratum

Corrigendum to Acta Cryst. (2009), E65, o610–o611

2-O-Benzhydryl-3,4-(S)-O-benzyl­idene-d-xylono-1,4-lactone

X-ray crystallography unequivocally shows that protection of the free hydroxyl group of 3,5-O-benzyl­idene-d-xylono-1,4-lactone with diphenyl­diazo­methane proceeded smoothly to give the title compound, C25H22O5, with no accompanying epimerization. Unlike the analogously protected lyxono lactone, the isomeric xylono lactone has two mol­ecules present in the asymmetric unit (Z′ = 2). The 5-ring lactones adopt envelope conformations and the 6-ring ketals adopt chair conformations

6-Deoxyhexoses froml-Rhamnose in the Search for Inducers of the Rhamnose Operon: Synergy of Chemistry and Biotechnology

In the search for alternative non‐metabolizable inducers in the l ‐rhamnose promoter system, the synthesis of fifteen 6‐deoxyhexoses from l ‐rhamnose demonstrates the value of synergy between biotechnology and chemistry. The readily available 2,3‐acetonide of rhamnonolactone allows inversion of configuration at C4 and/or C5 of rhamnose to give 6‐deoxy‐d ‐allose, 6‐deoxy‐d ‐gulose and 6‐deoxy‐l ‐talose. Highly crystalline 3,5‐benzylidene rhamnonolactone gives easy access to l ‐quinovose (6‐deoxy‐l ‐glucose), l ‐olivose and rhamnose analogue with C2 azido, amino and acetamido substituents. Electrophilic fluorination of rhamnal gives a mixture of 2‐deoxy‐2‐fluoro‐l ‐rhamnose and 2‐deoxy‐2‐fluoro‐l ‐quinovose. Biotechnology provides access to 6‐deoxy‐l ‐altrose and 1‐deoxy‐l ‐fructose

2-Azido-3,4;6,7-di-O-isopropyl­idene-α-d-glycero-d-talo-heptopyran­ose

In the title compound, C13H21N3O6, the six-membered ring adopts a twist-boat conformation with the azide group in the bowsprit position. The azide group is disordered over two sets of sites in a 0.642 (10):0.358 (10) ratio. The crystal structure consists of O—H⋯O hydrogen-bonded trimer units. The absolute configuration was determined from the use of d-mannose as the starting material

6-De­oxy-6-fluoro-d-galactose

The crystal structure unequivocally confirms the relative stereochemistry of the title compound, C6H11FO5. The absolute stereochemistry was determined by the use of d-galactose as the starting material. The compound exists as a three-dimensional O—H⋯O hydrogen-bonded network with each mol­ecule acting as a donor and acceptor for four hydrogen bonds