Kinetic acetalization for 1,2- and 1,3-diol protection by the reaction of p-methoxyphenylmethyl methyl ether with DDQ

Oikawa, Yuji; Nishi, Takao; Yonemitsu, Osamu

doi:10.1016/s0040-4039(00)88256-8

Cited by 71 publications

(31 citation statements)

References 10 publications

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“…This acetal was obtained exclusively in the illustrated epimeric form, presumably because the reaction leading to it operates under kinetic control. [6] In keeping with our recently reported studies on its bromo analogue, [7] when a tert-butyl methyl ether (TBME) solution of compound 3 was treated at -78°C with 6.5 mol-equiv. of DIBAl-H, then a ca.…”

Section: Resultssupporting

confidence: 73%

An Enantioselective Synthesis of the Epoxyquinol (+)‐Isoepiepoformin

et al. 2010

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Section: Resultssupporting

confidence: 73%

An Enantioselective Synthesis of the Epoxyquinol (+)‐Isoepiepoformin

et al. 2010

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“…The phases were separated, and the aqueous phase was extracted three times with 50 ml each of ether. The combined organic extracts were washed twice with 50 ml of brine, dried with MgS04, and concentrated in vacuo (13): To a suspension of 4.8 g (40 mmol) of potassium hydride in 50 ml of dry THF was added over 15 min 6.0 g (21 mmol) of (3R,4R,5S,6S)-6-(tert-butyldimethylsilyloxy)-3,5-dimethyl-l-octen-4-ol (12)') at 0°C. The mixture was stirred at room temperature until the evolution of hydrogen slowed down; 5 ml of DMF was added followed by 3.3 g (21 mmol) of freshly prepared p-methoxybenzyl chloride.…”

Section: (2e4s5s)-5-(tert-butyldimethylsiiy~oxy)-4-methyz-2-heptenesupporting

confidence: 89%

Stereoselective Synthesis of Alcohols, XXXVIII Stereoselective Total Synthesis of the Denticulatins

et al. 1991

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The total synthesis of the denticulatins 1 is described. Key feature is the efficient generation of the C-1-to-C-9 building block 37 by three consecutive stereoselective carbon -carbon bond-forming steps using chiral allylboronates. The C-lO-toMarine organisms have provided chemists with a large number of new natural products, many of which are derived from a polypropionate biogenetic pathway'). Among these products are the denticulatins A and B, which were isolated by Faulkner from Siphonaria denticdata 'I. The structures have been elucidated by a single-crystal X-ray analysis to be 1, differing in configuration at the epimerizable stereocenter at C-10. The absolute configuration was tentatively assigned from the sign of rotation of the degradation product 2 and was confirmed recently by the first total synthesis of the denticulatins by the group of Ziegler4). While the biological significance of the denticulatins is not fully known -these compounds are ichtyotoxic and may be involved as antifeedants -the chemistry of these compounds provides several challenges and questions: First of all, the denticulatins contain a hemiketal ring. They are therefore formally derived from the dihydroxy triketone 3, which could form two further hemiketals by addition of 7-C-17 building block was obtained by kinetic Sharpless resolution of an allylic alcohol followed by an Ireland-Claisen rearrangement.OH to either the C-11 or the C-3 carbonyl group. It was not known, how readily these hemiketals equilibrated and what the factors are that determine their relative stability. From the point of synthesis, the long sequence of contiguous stereocenters is a challenge, since an efficient synthesis would require the controlled generation of the stereogenic centers in the same steps that are used to build the molecular skeleton. For this purpose several strategies for the synthesis of such structures have been developed5) during the last decade, among which the aldol addition and the crotylmetal addition are most prominent. Nevertheless, the stereotriad Dn, occurring in many such polyketide natural products, is one which is still diflicult to attain by these methods. We therefore felt that a synthesis of the denticulatins would provide a severe and realistic test for our ability to efficiently synthesize such molecules by using the crotylboration technique. Our synthesis of denticulatin6) aimed at the construction of a protected equivalent of the aldehyde 4, containing all the relevant stereocenters, which was to be combined with the ketone 2. The same retrosynthetic scheme was the basis of Ziegler's synthesis of the denti~ulatins~). However, as will be shown below, stereoselective crotylboration afforded a much shorter access to the key aldehyde 4. DThe Synthesis of the Aldehyde 7, the C-1-to-C-9 Building BlockThe aldehyde 7 was considered to be a proper C-l-to-C-9 building block for the synthesis of the denticulatins. It was envisioned to be assembled by three consecutive stereoselective crotylboration sequences (Scheme 2).The first se...

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“…Adduct 3 was converted to the p -methoxy benzylidene acetal in 87% yield upon DDQ oxidation. 16 Finally, exposure of the alkenyl silane to pyridinium bromide perbromide gave the crude dibromide 5 , which was treated with sodium methoxide to furnish the alkenyl bromide 6 (Scheme 2). 17 …”

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confidence: 99%