Cycloalkylation reactions of 2-alkylthioindoles, (2; X = OSO₂R, halogens, or epoxy) to 2,3,4,9-tetrahydrothiopyrano[2,3-b]indoles (3)via the corresponding metallated indole intermediates have been studied. Compound (2) could be cyclized to (3) in good yield and regioselectivity on treatment with a Mg or Zn reagent, whereas Li, Na, and K reagents afforded (3) and/or its regioisomer. The leaving group (X) and the solvent were shown to be crucial for reactivity. The reaction of (2; X = OSO₂R as leaving group) and a Grignard reagent in non-polar solvents effectively afforded (3). The cyclization was demonstrated to proceed via an S_N2 process. Analyses of the ¹H and ¹³C NMR spectra of (3) revealed that the thiopyrano ring entity of (3) was anchored in a half-chair conformation which ensured that any C-4 substituent introduced was in the pseudoaxial position. Assignments for the ¹H and ¹³C signals of (3) are also reported.