A new synthetic route to β-bromoprop-2-ynyl mixed acetals and bromovinyl bis-allyl mixed acetals, precursors of α-methylene-γ-butyrolactones

Abstract

Cohalogenation by N-bromosuccinimide in methanol of (S-bromoallenyl ethers (3a-g) or ally1 allenyl ethers (8d-f) affords unsaturated halogeno-compounds (5a-g) or (9d-f) which are converted via homolytic carbocyclization into a-methylene-y-butyrolactones (7a-g).

Synthesis of 7a‐aryl‐5‐t‐butyl‐3‐methyleneoctahydrobenzofuran possessing partial skelotons of some santonin analogue and furanolignans by intramolecular radical cyclisation reaction

“…Thus the structure of the octahydrobenzofuran derivatives (1c-6c) is as shown in Figure 3. (7), 11, 13 -dehydroisohyposantonin (8), dihydrosesamin (9) and lariciresinol (10) that are possessed by 1c-6c.…”

“…Tetrahydrofuran derivatives possessing the partial skeletons of santonin (7), 11,13-dehydroisohyposantonin (8), dihydrosesamin (9) and lariciresinol (10) have been prepared in good yield by intramolecular radical cyclisation.…”

“…The hitherto unknown radical precursors, 1b-6b were prepared by a procedure similar to that reported [10] earlier from the corresponding 4-t-butyl-1-arylcyclo-Vol 44 hexenes (1a-6a) by treatment with N-bromosuccinimide and propargyl alcohol at -15°C to room temperature in good yield ( Treatment of the above bromopropynyl ethers, 1b-6b with n-Bu 3 SnH in presence of catalytic amount of AIBN in refluxing benzene for 6 hrs furnished the corresponding tetrahydrofuran derivatives (1c-6c) (Scheme 1). The crude residue of the reaction was contaminated with the tri-butyl tin hydride residue as evident from its 1 H NMR spectra.…”

“…Bicyclic octahydrobenzofuran derivatives (1c-6c) possessing the partial skeletons of santonin (7), 11,13-dehydroisohyposantonin (8), dihydrosesamin (9) and lariciresinol (10) have been synthesised by intramolecular radical cyclisation in good yield via the precursors viz., the trans diaxial bromopropynyl ethers (1b-6b) obtained in highly regio/stereoselective manner.…”

α-Alkylidene-γ-butyrolactone synthesis via one-pot C–H insertion/olefination: substrate scope and the total synthesis of (±)-cedarmycins A and B

“…(3aSR,8aRS)-3-Methyleneoctahydro-2H-cyclohepta[b]furan-2-one (trans-12aa) 33 and (3aRS,8aRS)-3-methyleneoctahydro-2H-cyclohepta[b]furan-2-one (cis12aa)34 …”