Premium
The Diels‐Alder Reactivity of 2,2′‐Ethylidenebis[3,5‐dimethylfuran] and Exploratory Chemistry of the Mono‐adducts
Author(s) -
Ancerewicz Jacek,
Vogel Pierre,
Schenk Kurt
Publication year - 1996
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/hlca.19960790514
Subject(s) - chemistry , adduct , acetal , substituent , medicinal chemistry , silylation , furan , reactivity (psychology) , stereoselectivity , cyclohexene , stereochemistry , organic chemistry , catalysis , alternative medicine , medicine , pathology
In the presence of Me 3 Al, 1‐cyanovinyl acetate added to 2,2′‐ethylidenebis[3,5‐dimethylfuran] ( 1 ) to give a 20:10:1:1 mixture of mono‐adducts 4,5,6 , and 7 resulting from the same regiocontrol (‘ para ’ orienting effect of the 5‐methyl substituent in 1 ). The additions of a second equiv. of dienophile to 4–7 were very slow reactions. The major mono‐adducts 4 (solid) and 5 (liquid) have 2‐ exo ‐carbonitrile groups. The molecular structure of 4 (1 RS ,1′ RS ,2 SR ,4 SR )‐2‐ exo ‐cyano‐4‐[1‐(3,5‐dimethylfuran‐2‐yl)ethyl‐7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐ endo ‐yl acetate) was determined by X‐ray single‐crystal radiocrystallography. Mono‐adducts 4 and 5 were saponified into the corresponding 7‐oxanorbornenones 8 and 9 which were converted with high stereoselectivity into (1 RS ,1′ SR ,4 RS ,5 RS ,6 RS )‐4‐[1‐(3,5‐dimethyl furan‐2‐yl)ethyl]‐6‐ exo ‐methoxy‐1,5‐ endo ‐dimethyl‐7‐oxabicyclo [2.2.1]heptan‐2‐one dimethyl acetal ( 12 ) and its (1′ RS ‐stereoisomer 12a , respectively. Acetal hydrolysis of 12a followed by treatment with ( t ‐Bu)Me 2 SiOSO 2 CF 3 led to silylation and pinacol rearrangement with the formation of (1 RS ,1′ RS ,5 RS ,6 RS )‐4‐[( tert ‐butyl)dimethy lsilyloxy]‐1‐(3,5‐dimethylfuran‐2‐yl)ethyl]‐5‐methoxy‐6‐methyl‐3‐methylidene‐ 2‐oxabicyclo[2.2.1]heptane ( 16 ). In the presence of Me 3 Al, dimethyl acetylenedicarboxylate added to 12 giving a major adduct 19 which was hydroborated and oxidized into (1 RS ,1′ RS ,2″ RS ,3″ RS ,4 SR ,4″ RS ,5 SR ,6 SR )‐dimethyl 5‐ exo ‐hydroxy‐4,6‐ endo ‐dimethyl‐1‐[1‐(3‐ exo ,5,5‐trimeth oxy‐2‐ endo ,4‐dimethyl‐7‐oxabicyclo[2.2.1]hept‐2‐yl)ethyl]‐7‐oxabicyclo [2.2.1]hept‐2‐ene‐2,3‐dicarboxylate ( 20 ). Acetylation of alcohol 20 followed by CC bond cleavage afforded (1′ RS ,1″ SR ,2 RS ,2′ ″SR ,3 RS , 3″ SR ,4 RS ,4″ SR ,5 RS )‐dimethyl {3‐acetoxy‐2,3,4,5‐tetrahydro‐2,4‐dimethyl‐5‐[1‐(3‐ exo ,5,5‐trimethoxy −2‐ endo ,4‐dimethyl‐7‐oxabicyclo[2.2.1]hept‐1‐yl)‐ethyl]furan‐2,5‐diyl} bis[glyoxylate] ( 24 ).