Pectenotoxin-2 Synthetic Studies. 1. Alkoxide Precoordination to [Rh(NBD)(DIPHOS-4)]BF₄ Allows Directed Hydrogenation of a 2,3-Dihydrofuran-3-ol without Competing Furan Production

Abstract

[reaction: see text] The alkoxide-directed hydrogenation shown is reported as a key step in a concise synthesis of a fully functionalized precursor to the C29-C40 F/G sector of pectenotoxin-2.

Stereoselective Aldol‐Type Cyclization Reaction Mediated by Dibutylboron Triflate/Diisopropylethylamine.

“…Compound 14: 1 H NMR (500 MHz, CDCl 3 ): δ 7.78-7.65 (m, 4H), 7.45-7.37 (m, 6H), 4.84 (s, 1H), 4.77 (s, 1H), 4.06 (m, 1H), 3.91-3.81 (m, 2H), 3.01 (d, J = 2.2 Hz, 1H), 2.25 (dd, J = 13.9, 8.1 Hz, 1H), 2.16 (dd, J = 13.9, 5.5 Hz, 1H), 1.77 (s, 3H), 1.73-1.69 (m, 2H), 1.05 (s, 9H).…”

“…Compound 15: 1 Compound 16: 1 Compound 17: 1 Hz, 1H), 4.0-3.91 (m, 2H), 3.79 (s, 3H), 2.44 (dd, J = 14.0, 6.6 Hz, 1H), 2.24 (dd, J = 14.0, 6.3…”

Stereoselectivity of the hydrogenation of galactofuranosyl exoglycals

“…6,7 The addition of hydrogen usually occurs from the same face of a cyclic system than the directing group. 8,9 Thus, we developed the chemistry to differentiate the 2-and the 3-positions of the starting exoglycal and selectively install a hindering group, or a OH group, on either face of the carbohydrate (Scheme 1). .…”

Synthesis of the FG Fragment of the Pectenotoxins

“…A synthesis of an FG-ring fragment has previously been reported from the laboratories of Murai et al 15,16 in which the main backbone of the FG rings was prepared by reaction of an anion generated from a chiral a-lithio tetrahydrofuranyl ring, representing the F ring, with a five-carbon aldehyde fragment. Studies toward the F ring have also emanated from the work of Paquette et al 17,18 who employed an elegant hydroxyl-directed hydrogenation of a dihydrofuran to generate the desired chirality present in the tetrahydrofuran F ring.…”