Functionalised bicyclic exo-glycals are readily obtained by base-catalysed (typically MeONa in MeOH) alkynol cycloisomerisation of ethynylated cyclic saccharides. Thus, base treatment of the phenylethynyl- and halogenoethynylated 1-O-acetyl-ribofuranoses 22 - 24 and the 4-ethynylated 1-thioglucopyranosides 30 - 33 gave - after deacetylation - selectively the (Z)-configured exocyclic enol ethers 26 - 28 (84 - 91%) and 34 - 37 (63-76%), respectively, resulting from a trans-5-exo-dig cyclisation. The ring closure to the trans-dioxahex-ahydroindans 34 - 37 is favoured by a concerted intramolecular protonation of the intermediate vinyl anion by the neighbouring HO-C(3). Cycloisomerisation of the 6-O-acetyl-4-(phenylethynyl)-1-thio-α-D-glucopyrano-side 39 occurred via the corresponding phenylethynylated allenes to provide the galacto-configured (Z)- and (E)-cis-dioxahexahydroindans 40 (30%) and 41 (51%). Surprisingly, the HO-C(4) unprotected α-D-galactopyranosyl-butα-1,3-diyne 15 and the β-D-glucopyranosyl-butα-1,3-diyne 51 (and its 2-bromoethynyl analogue) undergo a 6-exo-dig ring closure to the 2,5-dioxabicyclo[2.2.2] octanes 16 - 19 and 52/53, respectively, the ring closure requiring a boat conformation (B1,4 for 15, 1,4B for 51). Ring strain (anti-reflex effect) prevents an alkynol cycloisomerisation of 4-(phenylbuta-1,3-diynyl, bromoethynyl, or iodoethynyl) levoglucosan 56 - 59, and 56 reacted by elimination to the hex-1-ene-3,5-diyne 59 (82%), while isomerisation of 57 and 58 led to epimeric mixtures of the haloallenes 60 (82%) and 61 (68%).