3-Butenyl-isoxazolines were known as good precursors for the syntheses of new types of 5-cyanomethyl-2iodomethyltetrahydrofuran derivatives. 5-Cyanomethyl-2iodomethyltetrahydrofuran was synthesized from isoxazolines by electrophilic iodoetheration using iodine or iodine monochloride, which was the first example of electrophilic cleavage of isoxazoline ring by iodoetheration reaction. From the combination of this reaction and diastereoselective formation of isoxazoline in the support of magnesium chelation effect, we synthesized 5-cyanomethyl-3-hydroxy2-iodomethyltetrahydrofuran from syn-5-(1-hydroxy-3butenyl)isoxazolines with diastereoselctivity. We expected better diastereoselectivity could be achieved by adding one more hydroxyl group at the 2-position of butenyl group in isoxazoline close to the reaction center. First, we prepared chiral 3-diphenylmethyl-5-(1,2-dihydroxy-3-butenyl)isoxazolines (3) by 1,3-dipolar cycloaddition reaction of diphenylacetohydroximoyl chloride (1) with (3R,4R)-1,5hexadiene-3,4-diol (2a) and meso-1,5-hexadiene-3,4-diol (2b) by the aid of magnesium chelation effect, and after Oprotection of isoxazolines, iodoetheration was examined to synthesize chiral 5-cyanomethyl-3,4-dihydroxy-2-iodomethyltetrahydrofurans 6. Diphenylacetohydroximoyl chloride (1), precursor of diphenylacetonitrile oxide was reacted with (3R,4R)-1,5hexadiene-3,4-diol (2a) in the presence of ethylmagnesium bromide as shown in Scheme 1. The more ethylmagnesium bromide was used, the more diadduct 4a was formed in this reaction. When 2.2 equiv of ethylmagnesium bromide was used, the best result of 3a was obtained (Entry 3 in Scheme 1). In case of meso-1,5-hexadiene-3,4-diol (2b), however, only 47% of 3b was obtained (Entry 4 in Scheme 1). The isolated 3a was a single stereoisomer that thought to be synisomer of 5-position and a-position due to the magnesium chelation effect, but 3b must be a racemic mixture of synisomers according to which double bond was reacted. The hydroxyl groups of 3a were protected with TBDMS and MOM group, and then reacted with iodine monochloride in dichloromethane to give 5-cyanomethyl-3,4dihydroxy-2-iodomethyltetrahydrofurans 6 in moderate yields as shown in Scheme 2. 5a (P=TBDMS) afforded only trans-6a (P=TBDMS) without any trace of cis-6a (P=TBDMS), while 5a (P=MOM) afforded a mixture of two isomers (trans/cis, 5/1). As we expected, the bulkier TBDMS group showed better diastereoselectivity in iodoetheration. We examined the energy minimizations of trans-