Ethoxycarbonylmethylenetriphenylphosphorane in carbohydrate chemistry, part II: a short and efficient synthesis of (+)-goniofufurone

Study of Stereoselectivity in Organometallic Additions to 1,2-O-Isopropylidene-O-R-α-D-xylopentodialdo-1,4-furanose

“…Treatment of aldehydes 6 with phenyl magnesium bromide in THF (see Table 1, Entry 1) or diethylether (Entries 2-4) gave in all cases the Lido diastereomer 8 as a major product as a result of 1,2-chelation-control. The highest degree of selectivity found for 6b is in accordance with the literature [6,[9][10][11][12], whilst aldehydes 6c and 6d with silyl (known for its non-chelation nature) and mesyl group (with opposite effect) gave about equal amounts of both diastereomers 7 and 8.…”

“…The absolute configuration at the newly formed stereocentre, and hence the configuration of alcohols 7b and 8b, was established by comparison of 1 H-, 13 C-NMR data, and specific rotations with those described in the literature [6,[9][10][11][12]. The structures of 7a/ 8a were established by total synthesis of (+)-1, (+)-2 [3].…”

On the nature of the electronic effect of multiple hydroxyl groups in the 6-membered ring – the effects are additive but steric hindrance plays a role too

“…12 : 1 ratio of the epimers (9 and 13), with L-ido (13) being the major product. 17 Since both were required, a twostep conversion of 13 involving PDC oxidation and NaBH 4 reduction provided the D-gluco derivative 9 as the main product (approx. 10 : 1 over 13).…”

Synthesis and antibiotic activity of the tricyclic furo[3,2-c] isochromen-2-trione unit of the pyranonaphthoquinones

“…Interestingly, Martı´n and co-workers have recently shown in analogous systems that when the E-isomers undergo oxaMichael cyclization, cis-substituted pyran derivatives are preferentially obtained, while cyclization of the Z-olefins give rise mainly to the trans-substituted oxacycles. 22 Protection of the benzylic alcohol in 18 proved to be crucial to the success of the sequence, because it prevented hydroxyl group participation in side reactions 23 during the lactone reduction and Wittig olefination steps and also improved stereochemical control of the oxa-Michael product. Simultaneous experiments carried out without protection of 18 evidenced difficulties in accomplishing the reduction of this hydroxylactone and lead to a 1.15:1 mixture of 23 and 24 in 16% overall yield.…”