Question

R. R. Gadikota et al. / Tetrahedron: Asymmetry 14 (2003) 737-742 739 오 Lo -. LOWOH a, b 10. 16 FO c - Lo e, f L Ho" OH TBDPSO | 01 d| RO 19, R = H 20, R = TBDPS i, j, k TBDPSO

9. In the conversion of 17 to 18 why does the acetal form between C2-C3 and C5-C6 rather than

C4-C5 or C3-C4?

1. What are 4Å molecular sieves? (Used in synthesis of 11) (Cite your source)

2. How was 11 purified?

3. What is the appearance of 14?

Answer 1

Solution:

9. Answer: Since in this reacction step first ring opening of glucose is hapapened to produce a fructofuranose intermediate which was further reaacted with the acetone to get protected of syn-diols as presented in below scheme. Since C3 and C4 are anti in the structure of glucose and C4 is having -OH group but not on C5 hence there must not a possibility of protection by acetone. When we consider a saw horse projection of glucose C4 and C5 have -OH groups and those -OH can be syn but indeed cyclic form of glucose is more stable than saw horse projection stucture. In general glucose is exist in the form of cyclic only. Hence possibilities of acetone protection at C4 and C5 is eliminated.

OOH H2SO4 HOA Нолоон PHỐ HO HO HO Voymom OH HO HOY OH OH Ho You OH OH Glucose Ring opening но Но, он Но он о CH OH HOHн HO -Н НЕОН HOH OWOH HO Ring formation YOH HOOH H2SO4/Acetone/ CuSO4 Сон , он These two-OH groups also can be self arranged as syn 1,2-diols. A single bond between C5 and C6 easily rotate hence -OH attached to C6 can be arranged in syn position to -OH attached to C5 - HOH Ho 5 OOH Oxidation PCC HO 2 OH These two are syn 1,2-diols Mechanism for acetonide protection HT 00 чон I HOH OH но Но, он HO HOVO HOOH HU OH HOOH HH OH OH H+/Acetone IT OH Но он

1. What are 4Å molecular sieves? (Used in synthesis of 11) (Cite your source)

Answer: Molecular sieve is a silica-alumina having formula of Na12[(AlO2)12(SiO2)12]•X H2O. 4A Molecular sieve is having mesh size of 4 angstrom.In the laboratory 4A Molecular Sieve is used for removing moisture from solvents.

In connection with the current question, 4A Molecular Sieve is used for the removing or abosrption of moisture from THF solvent to maintain the dry condition in reaction.

2. How was 11 purified?

Answer: Compound 11 is purified using column chromatography using 6:1 hexane: ethyl acetate eluent. A silica gel filled column is used to perform this purification and product 11 is eluted in 6:1 hexane: ethyl acetate solvent system.

3. What is the appearance of 14?

Answer: Appearance of compound 14 is Pale Yellow colored and nature of this compound is Oil.

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