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Asymmetric Synthesis of Complicated Bicyclic and Tricyclic Polypropanoates via the Double Diels‐Alder Addition of 2,2′‐Ethylidenebis[3,5‐dimethylfuran]
Author(s) -
Marchionni Chiara,
Vogel Pierre
Publication year - 2001
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(20010228)84:2<431::aid-hlca431>3.0.co;2-w
Subject(s) - chemistry , stereocenter , bicyclic molecule , stereochemistry , desymmetrization , enantioselective synthesis , ring (chemistry) , adduct , hydroboration , catalysis , organic chemistry
A new, non‐iterative method for the asymmetric synthesis of long‐chain and polycyclic polypropanoate fragments starting from 2,2′‐ethylidenebis[3,5‐dimethylfuran] ( 2 ) has been developed. Diethyl (2 E ,5 E )‐4‐oxohepta‐2,5‐dienoate ( 6 ) added to 2 to give a single meso ‐adduct 7 containing nine stereogenic centers. Its desymmetrization was realized by hydroboration with (+)‐IpcBH 2 (isopinocampheylborane), leading to diethyl (1 S ,2 R ,3 S ,4 S ,4a S ,7 R ,8 R ,8a R ,9a S ,10 R ,10a R )‐1,3,4,7,8,8a,9,9a‐octahydro‐3‐hydroxy‐2,4,5,7,10‐pentamethyl‐9‐oxo‐2 H ,10 H ‐2,4a : 7,10a‐diepoxyanthracene‐1,8‐dicarboxylate ((+)‐ 8 ; 78% e.e.). Alternatively, 7 was converted to meso ‐(1 R ,2 R ,4 R ,4a R ,5 S ,7 S ,8 S ,8a R ,9a S ,10 s ,10a S )‐1,8‐bis(acetoxymethyl)‐1,8,8a,9a‐tetrahydro‐2,4,5,7,10‐pentamethyl‐2 H ‐10 H ‐2,4a : 7,10a‐diepoxyanthracene‐3,6,9(4 H ,5 H ,7 H )‐trione ( 32 ) that was reduced enantioselectively by BH 3 catalyzed by methyloxazaborolidine 19 derived from L ‐diphenylprolinol giving (1 S ,2 S ,4 S ,4a S ,5 S ,6 R ,7 R ,8 R ,8a S ,9a R ,10 R ,10a S )‐1,8‐bis(acetoxymethyl)‐1,8,8a,9a‐tetrahydro‐6‐hydroxy‐2,4,5,7,10‐pentamethyl‐2 H ,10 H ‐2,4a : 7,10a‐diepoxyanthracene‐3,9(4 H ,7 H )‐dione ((−)‐ 33 ; 90% e.e.). Chemistry was explored to carry out chemoselective 7‐oxabicyclo[2.2.1]heptanone oxa‐ring openings and intra‐ring C−C bond cleavage. Polycyclic polypropanoates such as (1 R ,2 S ,3 R ,4 R ,4a R ,5 S ,6 R ,7 S ,8 R ,9 R ,10 R ,11 S ,12a R )‐1‐(ethoxycarbonyl)‐1,3,4,7,8,9,10,11,12,12a‐decahydro‐3,11‐dihydroxy‐2,4,5,7,9‐pentamethyl‐12‐oxo‐2 H ,5 H ‐2,4a : 6,9 : 6,11‐triepoxybenzocyclodecene‐10,8‐carbolactone ( 51 ), (1 S ,2 R ,3 R ,4 R ,4a S ,5 S ,7 S ,8 R ,9 R ,10 R ,12 S ,12a S )‐1,10‐bis(acetoxymethyl)tetradecahydro‐8‐(methoxymethoxy)‐2,4,5,7,9‐pentamethyl‐3,9‐bis{[2‐(trimethylsilyl)ethoxy]methoxy}‐6,11‐epoxycyclodecene‐4a,6,11,12‐tetrol ((+)‐ 83 ), and (1 R ,2 R ,3 R ,4a R ,4b R ,5 S ,6 R , 7 R ,8 R ,8a S ,9 S ,10a R )‐3,5‐bis(acetoxymethyl)‐4a,8a‐dihydroxy‐1‐(methoxymethoxy)‐2,6,8,9,10a‐pentamethyl‐2,7‐bis{[2‐(trimethylsilyl)ethoxy]methoxy}dodecahydrophenanthrene‐4,10‐dione ( 85 ) were obtained in few synthetic steps.