TY - JOUR
T1 - Synthesis of exo enol ether-cyclic ketal isomers of substituted furanmethanol structures related to marine furanocembranoids
AU - Li, Yi
AU - Pattenden, Gerald
AU - Rogers, Joseph
N1 - Funding Information:
We thank the EPSRC for a Fellowship (to Y.L.) and for a Studentship (to J.R.). We also thank Merck for support, and Bencan Tang and Amael Veyron for some initial studies in this area.
PY - 2010/3/3
Y1 - 2010/3/3
N2 - Oxidations of the 2-alkenylfurans 8a and 8b, using peroxy reagents, lead to the dienedione 9 and the furan epoxide 10, respectively. Treatment of the epoxide 10 with p-TSA in MeOH produces the enol ether cyclic ketal 12, which is rapidly isomerised to the furanmethanol ether 15, isolated in 80% yield. By contrast, when the propanol-substituted furan epoxide 23 was kept in CDCl3 containing traces of HCl for 2 h, a 3:2 mixture of Z- and E-isomers of the enol ether spiro ketals 25a and 25b was produced in >92% yield; after 24 h this mixture of isomers underwent dehydration leading to the corresponding enol ether triene 26 (70%). When a solution of the dienedione 9 in H2O-THF containing p-TSA was stirred at 25 °C for 20 h, the tertiary alcohol 27 was produced which, after a further 20 h was converted into the furan vicinal diol 29. Likewise, when the 'cembranoid' dienedione 31 was treated with p-TSA-H2O, the hydroxymethyl-substituted furanobutenolide 33 was produced in 40% yield. It is probable that the enol ether cyclic hemiketals 28 and 32/34, which are related to 12 and 25, and also to the naturally occurring cembranoids 1 and 2 found in corals, are transient intermediates in the conversions leading to 29 and 33 from 9 and 31, respectively.
AB - Oxidations of the 2-alkenylfurans 8a and 8b, using peroxy reagents, lead to the dienedione 9 and the furan epoxide 10, respectively. Treatment of the epoxide 10 with p-TSA in MeOH produces the enol ether cyclic ketal 12, which is rapidly isomerised to the furanmethanol ether 15, isolated in 80% yield. By contrast, when the propanol-substituted furan epoxide 23 was kept in CDCl3 containing traces of HCl for 2 h, a 3:2 mixture of Z- and E-isomers of the enol ether spiro ketals 25a and 25b was produced in >92% yield; after 24 h this mixture of isomers underwent dehydration leading to the corresponding enol ether triene 26 (70%). When a solution of the dienedione 9 in H2O-THF containing p-TSA was stirred at 25 °C for 20 h, the tertiary alcohol 27 was produced which, after a further 20 h was converted into the furan vicinal diol 29. Likewise, when the 'cembranoid' dienedione 31 was treated with p-TSA-H2O, the hydroxymethyl-substituted furanobutenolide 33 was produced in 40% yield. It is probable that the enol ether cyclic hemiketals 28 and 32/34, which are related to 12 and 25, and also to the naturally occurring cembranoids 1 and 2 found in corals, are transient intermediates in the conversions leading to 29 and 33 from 9 and 31, respectively.
UR - http://www.scopus.com/inward/record.url?scp=74849115406&partnerID=8YFLogxK
U2 - 10.1016/j.tetlet.2009.12.131
DO - 10.1016/j.tetlet.2009.12.131
M3 - Article
AN - SCOPUS:74849115406
SN - 0040-4039
VL - 51
SP - 1280
EP - 1283
JO - Tetrahedron Letters
JF - Tetrahedron Letters
IS - 9
ER -