Annulation with furan synthesis of benzofurans

Hexa hydro-3,4-d ioxobenzo[b] fura n 85 was obtained by intramolecular nucleophilic heterocyclization of 2-chloroacetyl-5,5-dimethylcyclohexane-1,3-dione 84 (85KGS1130). Cyclization was also achieved in the presence of sodium nitrite, sodium methoxide, sodium acetate, or silver acetate. The nucleophiles acted as basic deprotonating agents and did not interact with the chloroacetyl group (89ZOR1882). 

The ethyl ether of 1 was obtained by reaction of 1 with ethanol in boiling benzene in the presence of p-toluonesulfonic acid. A Stork-Danheiser alkylation of which with lithium diispropylamide and methyl iodide and then with ethyl bromoacetate gave 93. Reduction of 93 with 

Three-component condensation reactions of cyclic 1,3-diketones, 4-nitrobenzaldehyde, and alkyl or aryl isocyanides in water afforded the corresponding tetrahydrobenzofuran derivatives (04M441). 

2-Nitro-propene or 2-butene and 1 gave ketofuran adduct 130 and 131 (R = Me), respectively (75CC726, 80JOC2945). A stereoisomeric mixture of hydroxyimino dihydrofuran 132 was obtained in the presence of KE Reaction of 1 with l-nitro-l-(phenylthio)-propene in the presence of KF afforded a diastereomeric mixture of dihydrofuran 133 along with 

3- methyltetrahydrobenzofuran 131 (R = H) (80JOC2945), that was obtained when 1 was treated with diethylprop-2-ynylsulfonium bromide (93JOC3960, 94JOC5970). l-Bromo-2-(p-chlorophenyl)-l-nitroethene with 1 gave 3-(p-chlorophenyl)-2-nitro-2,3,4,5,6,7-hexahydrobenzofuran-4-one 134. The reaction involved Michael addition to form an intermediate 

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