The fused heterocycle 4-(phenylsulfonyl)-4H-furo[3,4-b]indole, which is an indole-2,3-quinodimethane synthetic analogue, is prepared in five steps from indole in 46% yield. A similar sequence is used to synthesize C-3 derivatives (3-methyl, 3-phenyl, and 3-heptyl). Thus, indole-3-carbaldehyde (1) is protected as the N-phenylsulfonyl derivative 2 and converted to the ethylene acetal 6. Lithiation at C-2 followed by treatment with an aldehyde affords the expected hydroxy acetals 7 and 8. Exposure to acid effects cyclization to the furoindoles 5 and 9. Furthermore, C-1 lithiation of furo[3,4-b]indole 9c followed by treatment with methyl iodide affords disubstituted furo[3,4-b]indole 10.

中文翻译：

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有效合成4-（苯磺酰基）-4H-呋喃并[3,4-b]吲哚。

稠合的杂环4-（苯磺酰基）-4H-呋喃[3,4-b]吲哚是吲哚-2,3-喹二甲烷合成类似物，由吲哚经五步制备，收率为46％。类似的序列用于合成C-3衍生物（3-甲基，3-苯基和3-庚基）。因此，吲哚-3-甲醛（1）被保护为N-苯基磺酰基衍生物2并转化为乙缩醛6。在C-2处锂化，然后用醛处理，得到了预期的羟基缩醛7和8。影响呋喃并吲哚5和9的环化反应。此外，呋喃[3,4-b]吲哚9c的C-1锂化反应，然后用碘甲烷处理，得到二取代的呋喃[3,4-b]吲哚10。