Richard H. Wightman

Assignment of ring size in isopropylidene acetals by carbon-13 n.m.r. spectroscopy

Abstract The 13 C-n.m.r. spectra of a range of isopropylidene acetals of carbohydrates have been studied. Attention has been focussed on the chemical shifts of the acetal carbon and methyl groups of the acetals. These parameters are characteristic of ring-size (1,3-dioxolane, 1,3-dioxane, and 1,3-dioxepane) and can sometimes give further information on ring-fusions and conformations. An example is given of the application of the method to 1,3:2,4:5,6-tri- O -isopropylidene- d -glucitol.

Hydroxylated pyrrolidines. Synthesis of 1,4-dideoxy-1,4-imino-L-lyxitol, 1,4,5-trideoxy-1,4-imino-D- and -L-lyxo-hexitol, 2,3,6-trideoxy-3,6-imino-D-glycero-L-altro- and -D-glycero-L-galacto-octitols, and of a chiral potential precursor of carbapenem systems

Abstract Enantiospecific syntheses are reported for the title pyrrolidines, from carbohydrate precursors. An intermediate in one of the routes, ethyl 2,3,6-trideoxy-3,6-imino-4,5:7,8-di- O -isopropylidene-D- glycero -L- altro -octonate ( 23 ), could be converted in two steps into a β-lactam.

Synthesis of trihydroxylated pyrrolizidines and indolizidines using cycloaddition reactions of functionalized cyclic nitrones, and the synthesis of (+)- and (-)-lentiginosine

Abstract Cycloadditions of 3,4-isopropylidenedioxy-Δ1-pyrroline-1-oxide (9), (3S,4S)-3,4-bis(methoxymethoxy)-Δ1-pyrroline-N-oxide (28), and its (3R,4R)-enantiomer, with suitably-functionalized alkenes has led to the synthesis of the 1,2,6-trihydroxypyrrolizidines 14, 33 and ent-33, and the 1,2,7-trihydroxyindolizidines 22,39 and ent-39. Deoxygenation of two enantiomeric intermediates in these syntheses led to the preparation of the dihydroxylated indolizidine (+)-lentiginosine and its (−)-enantiomer.

Hydroxylated pyrrolizidines and indolizidines; synthesis using cycloaddition reactions of functionalized cyclic nitrones

Abstract Cycloaddition reactions of functionalised Δ 1 -pyrroline- N -oxides have been used to prepare the hydroxylated pyrrolizidines 11 and 22 , the indolizidine 16 , and the iminoheptitol 12 .

Assignment of ring size in isopropylidene acetals by 13C N.M.R.

Cyclic isopropylidene acetals containing 5,6 and 7-membered rings can be distinguished by measurement of the 13C chemical shifts of the acetal carbon and the methyl groups.

Reactions of 2,3-O-isopropylidene derivatives of furanose sugars with organomagnesium and organolithium nucleophiles

Abstract Reactions of 2,3- O -isopropylidene derivatives of furanose sugars with Grignard reagents afford stereoselectively products with an anti- ( erythro -) relationship between the new chiral centre and that at C-2; the corresponding reactions with organolithium reagents are more variable stereochemically, but some predictive guidelines can be established.

Synthesis of some pyrrolo[2,3-d]pyrimidine and 1,2,3-triazole isonucleosides

Abstract Nucleoside analogues 8,9,10 and 11, in which a pyrrolo[2,3-d]pyrimidine ring is linked to a 2-hydroxymethyl-3-hydroxytetrahydrofuran, have been prepared. The azide 16 used as an intermediate in the routes to these compounds also gave access to the 1,2,3-triazole isonucleosides 12 and 13.

Hydrogenolysis of enol triflates; A new method for the reduction of ketones to methylene compounds

Abstract Hydrogenolysis of enol trifluoromethanesulphonates (enol triflates) gives the hydrocarbon in high yield; ketones can thus be converted to the corresponding methylene compounds in a two-step process under mild conditions.

The enantiospecific synthesis of (4S,5R)-and (4S,5S)-4,5-dihydroxydecanoic acid γ-lactones, proposed autoregulators from Streptomyces griseus

Abstract Both the (4S,5R)- and (4S,5S)-isomers of 4,5-dihydroxydecanoic acid γ-lactone, natural products and proposed autoregulators of Streptomyces Griseus, have been synthesised directly and in high yield from D-ribose via a common intermediate.

Enantiospecific synthesis of (-)-5-epi-shikimic acid and a new route to (-)-shikimic acid

Abstract (-)-Shikimic acid ( 1 ) and (-)-5- epi -shikimic acid ( 2 ) have each been prepared enantiospecifically and with high diastereoselectivity from D-ribose.