Various β-, γ-, and δ-alkynols have been reacted with the cedented seven-membered oxacarbene ring. The rheniumassisted δ-alkynol to 2-oxacyloheptylidene rearrangement 16e Ϫ fragment [(triphos)Re(CO) 2 ] + generated in situ by H 2 elimination from [(triphos)Re(CO) 2 (η 2 -H 2 )]BF 4 [triphos = proceeds via the hydroxybutylvinylidene kinetic intermediate [(triphos)Re(CO) 2 {C=C(H)CH 2 CH 2 CH 2 CH 2 OH}]BF 4 , MeC(CH 2 PPh 2 ) 3 ]. Irrespective of the length of the alkyl chain between the CϵC and OH functional groups in the ω-alkywhich has been characterized in both the solid state and solution. An X-ray analysis has been carried out on a single nol, 2-oxacyclocarbene complexes are obtained. These include the 2-oxacyclopentylidene derivatives [(triphos)-crystal of [(triphos)Re(CO) 2 {=CCH 2 CH 2 CH(Me)O}]BF 4 . The structure of this complex consists of [(triphos)Re(CO) 2 {= Re(CO) 2 {=CCH 2 CH 2 CH 2 O}]BF 4 and [(triphos)Re(CO) 2 -{=CCH 2 CH 2 CH(Me)O}]BF 4 , the 2-oxacyclohexylidene dervi-CCH 2 CH 2 CH(Me)O}] + cations and tetrafluoroborate anions with no interspersed solvent molecules. A facial triphos li-vatives [(triphos)Re(CO) 2 {=CCH 2 CH 2 CH 2 CH 2 O}]BF 4 and [(triphos)Re(CO) 2 {=CCH 2 CH 2 CH 2 CH(Me)O}]BF 4 , and the 2-gand, two cis-disposed carbonyl groups and a 2-oxacyclopentylidene ligand coordinate the Re centre in a slightly di-oxacycloheptylidene complex [(triphos)Re(CO) 2 {=CCH 2 CH 2 -CH 2 CH 2 CH 2 O}]BF 4 . The latter compound contains a unpre-storted octahedral environment.