摘要：

J. CHEM. SOC. PERKIN TRANS. 1 1994 Synthetic Studies on Calyculin A: A Convenient Asymmetric Synthesis of anti-Vicinal Diols Anthony G. M. Barrett"ra and James W. Malecha* a Department of Chemistry, Imperial College of Science, Technology and Medicine, London SW7 2A Y, UK Department of Chemistry, Colorado State University, Fort Collins, Colorado, 80523, USA anti-Vicinal diols have been prepared with excellent relative and absolute stereocontrol via the reaction of aldehydes with 8-(3-[(diisopropylamino)dimethylsilyl]allyl}diisopinocampheylborane in THF and diethyl ether and work-up using potassium fluoride, potassium hydrogen carbonate and hydrogen peroxide in aqueous methanol. Absolute stereoselectivities of reactions were determined by conversion of four product diols into bis[ (R)-a-methoxy-a-(trifluoromethyl)phenylacetate] esters.The reactions are relevant to the synthesis of the marine phosphatase inhibitor calyculin A. The condensation of allylmetallic reagents with aldehydes represents a most powerful method for the stereocontrolled preparation of homoallylic alcohols.' For example, Brown and coworkers have introduced several monoterpene derived allyl- and crotyl-boranes that are especially useful in asymmetric synthesk2 These methods, which are exemplified by the con- version of boranes 1 and 3, respectively, into alcohols 2 and 4 (Scheme l), are particularly useful for the preparation of 4-hydroxy- and 4-hydroxy-3-methylalk- 1 -enes. In most cases, the products were formed with both excellent relative and absolute stereochemical control.In an adaptation of this chemistry, we have introduced B-[(E)-3-(diphenylamino)-allyl]diisopinocampheylborane 53 and B-[(E)-3-(diphenyl met h yleneamino)allyl]diisopinocampheylborane 6 and their respective antipodes for the highly stereoselective synthesis of anti-p-amino alcohols. In addition, we have repeatedly applied the Brown methods in the total synthesis of nikkomycin B and in approaches to the total synthesis of avermectin6 and caly- culin A 7.' Herein, we report experimental details of a convenient method * to prepare antiTvicinal diols using allyl- borane methodology. The method, which is an adaptation of Tamao chemistry,' has proven to be particularly useful for the stereospecific synthesis of the terminal amino acid unit of calyculin A 7.Elsewhere, Roush has reported an equivalent allylboronate methodology for the synthesis of related diol arrays. O Resultsand Discussion An ethereal solution of the allylsilane 8 was cooled to 0 "C and allowed to react with butyllithium and TMEDA. After 4 h, the yellow solution was cooled to -78 "C and (-)-B-methoxy- diisopinocampheylborane 13 in diethyl ether was added to it. After 1 h the solution, presumably containing the 'ate' complex 9, was treated with BF,-OEt, to generate the corresponding trialkylborane 10. This intermediate was not isolated but was allowed to react directly with benzaldehyde, followed by work- up with hydrogen peroxide under basic conditions.This resulted in the oxidative cleavage of the carbon-silicon bond in the intermediate lla, and hydrolysis of the boronate ester to reveal the anti-diol 12a in 50% overall yield (Scheme 2). Additionally, under identical reaction conditions, the antipodal borane reagent 14 gave the enantiomeric diol15a. The relative stereochemical assignments of the products 12a and 15a were determined by comparison of 'H NMR data with literature values for the corresponding racemic anti-diols. ' Both diols 12a and 15a showed 6 4.66 (d, 1 H, J 4.3 Hz) and 4.21 (m, 1 H) for the [CH(OH)CH(OH)] unit. This value is Me Me 1 2 70%,ds 991 88 90% 3 4 70%, ds 99:l -90% Scheme 1 Reugentsundconditions:i, EtCHO, -78 "C; ii, H,02, NaOH Table 1 Reactions of aldehydes with boranes 10 and 14 Entry Aldehyde Borane Products (%)" PhCHO 10 14 2-C,H,SCHO 10 14 CH,(CH,),CHO 10 c-C,H,,CHO 10 18 10 14 12a (50) 15a (47) 12b (44) 15b (47) 12c (46) 12d (45) 19 (57) 19 (30), 20 (15) Mosher ester (%)" 16a (83) 17a (79) 16b (95) 17b (82) C C C c " All products were formed with diaster

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