Methanol was one of the earliest molecules to be detected by means of radio astronomy. A plethora of reports deserve mentioning here. Therefore, this documentation may well be incomplete for quite a while.
J. A. Ball, C. A. Gottlieb, A. E. Lilley, and H. E. Radford
reported on the
Detection of Methyl Alcohol in Sagittarius
Astrophys. J. 162, L203–L210 (1970).
They used the 140-foot Greenbank radio telescope for the 1₁₀ – 1₁₁ transition near 834 MHz to detect methanol in emission from Sagittarius (Sgr) A and B2.

C. A. Gottlieb, J. A. Ball, E. W. Gottlieb, and D. F. Dickinson
reported on
Interstellar Methyl Alcohol
Astrophys. J. 227, 422–432 (1979).
They used the 11 m Kitt Peak radio telescope to search for the J = 2 – 1 transitions of CH₃OH, ¹³CH₃OH, and CH₃OD in the 3 mm region toward several galactic sources. CH₃OH was detected toward 14 sources, at least the majority of these are hot-core sources. The identification of ¹³CH₃OH lines toward Sgr B2 may well be correct (the ¹²C to ¹³C ratio of somewhat less than 10 is probably affected by opacity of the CH₃OH lines), but the identification of CH₃OD toward the same source is definitively incorrect; see for example:
A. Belloche, H. S. P. Müller, R. T. Garrod, and K. M. Menten
Exploring Molecular Complexity with ALMA (EMoCA): Deuterated Complex Organic Molecules in Sagittarius B2(N2)
Astron. Astrophys. 587, Art. No. A91 (2016).

F. F. Gardner, J. B. Whiteoak, J. Reynolds, W. L. Peters, and T. B. H. Kuiper
reported on the
First Detection of the ¹⁸O Isotope of Methanol
Mon. Not. R. Astron. Soc. 240, 35P–40P (1989).
The NASA's 70 m dish at Tidbinbilla was used to detect the J_K = 2₀ − 3₋₁ transition of CH₃¹⁸OH near 11.6 GHz toward Sgr B2. The derived ¹⁶O to ¹⁸O ratio of 210 ± 40 is in line with other results obtained toward the galactic center.

F. J. Lovas, R. D. Suenram, L. E. Snyder, J. M. Hollis, and R. M. Lees
reported on the
Detection of the Torsionally Excited State of Methanol in Orion A
Astrophys. J. 253, 149–153 (1982).
Three lines partaining to four transitions of torsionally excited methanol were detected with the 11 m Kitt Peak radio telescope at 3 mm.

Contributor(s): H. S. P. Müller; 04, 2022