Regioselective total synthesis of furoventalene, a marine natural

J. Org. Chem. 1981,46,4264-4266

4264

Regioselective Total Synthesis of Furoventalene, a Marine Natural Benzofuran, via the P-VinylbutenolideAnnulation Fusao Kido,' Yoshihiro Noda,l Takao Maruyama,' Chizuko Kabuto,2 and Akira Yoshikoshi*' Chemical Research Institute of Non-Aqueous Solutions and Department of Chemistry, Tohoku University, Sendai 980,Japan Received M a y 19, I981

The framework of furoventalene (1) was regioselectively constructed from methyl 2-fomy1-6-methyl-~heptenoate (12)and 2,5-dihydro-3-methyl-4-vinyl-2-furanone (10) by consecutive 1,6 conjugate addition and aldol-type cyclization to lead to a diastereomericmixture of bicyclic butenolidea 13a and 13b. Both of the annulation products were transformed into 1 by a sequence of reactions: reduction, hydrolysis, dehydrative decarboxylation, and dehydrogenation via intermediates 14-16. The stereochemistry of the annulation products 13a and 13b is also discussed. Scheme 1"

Furoventalene (1) is an irregular isoprenoid benzofuran isolated from the sea fan Gorgonia ~ e n t a l i n a . ~This compound was first synthesized by Weinheimer and Washecheck in a nonregioselective manner.3 -4-

'

I

a

7

-'-A

b)

-

+SPh

2

-

4

~

Lc/* 0

"1%

Recently, the new annulation reaction of 1,3-dicarbonyl compound 2 with P-vinylbutenolide (3), which is shown by the following equation (2 + 3 41, has been developed

3

~

Q3

BI*I.

'0

9

(1) EtC(OEt),, hydroquinone; ( 2 ) i-Pr,NLi, Ph,S,, HMPA, THF; (3)MCPBA, CH,CI,; ( 4 ) A , PhMe. 0

Scheme 11" Co2Me 11

--

- Y--fCOZH C ( 6 6 *I.

I

ti0

12