Substituted benzynes can be trapped intramolecularty by an attached furan moiety and such a reaction has been used in the synthesis of the natura'LZy occurring o-naphthoquinone mansonone E.
The intramolecular Diels-Alder reaction continues to enjoy considerable popularity, particularly in its application to the synthesis of natural products. 1 However, intramolecular Diels-Alder reactions of benzynes have, to our knowledge, not been previously reported.
This is surprising in view of the fact that intermolecular reactions between unsymmetrical benzynes and unsynrmetrical dienes exhibit little or no regioselectivityL and complete control of regiochemistry should be possible by linking the benzyne to the diene through a chain of suitable length. This is illustrated below for a system involving a substituted furan as the diene. The nature of the linkinggroupsx and Y would depend on the ultimate synthetic object-R'T, yRz-(CH2),, ive, i.e. whether or not disconnection of the chain linking the benzyne and furan moieties is necessary. We now report the use of such an approach in the synthesis of mansonone E 10, one of a series of naphthoquinones isolated from the wood of Mansonia attissima. 394 Alkylation of the phenol l5 with 2-chloroacetyl-5-methylfuran6 gave the ether 27 m.p. 115.5-116", which was converted into the acetal 3 m.p. 92.5-93.5", and thence into the substituted anthranilic acid 4, m.p. 153.5-154' in a standard manner. The anthranilic acid 4