Angular alkylation through intramolecular carbenoid insertion. New stereocontrolled route to synthetic intermediates to the diterpene alkaloids and C20-gibberellins

δ-Sultone Formation Through Rh-Catalyzed C−H Insertion

“…The bias for diazosulfonates to form six-membered-ring products is noted in entries 3−5, the latter two reactions yielding novel bridging bicyclic structures . Such transannular insertion events are less common with diazocarbonyl derivatives, and may prove serviceable for installing angular groups at fused carbon centers in complex polycylic natural products …”

Synthetic studies toward complex diterpenoids. IX. New stereocontrolled synthetic route to some intermediates for diterpenoid alkaloids and C20 gibberellins

“…The catalyst was filtered off and the solvent was evaporated under reduced pressure to afford a gummy solid which was chromatographed on neutral alumina (50 g) and eluted with petroleum ether to afford 8a as a white solid (1.25 g, 55%), mp 116-117 °C. Recrystallization from light petroleum gave the analytical sample: mp and mmp 117-118 °C (lit.6*1 mp 118 °C); ir (KBr) spectrum was identical with that of the sample previously prepared by a different route;6*1,18 Xmax 266 nm (log e 2.65), 274 (2.64); NMR (220 MHz) 1.045 (s, 3 H, -CH3), 1.20-1.75 (complex m, 9 H, -CH2 and -CH <), 2.32 (d, 1 H, JAB = 20 Hz), 2.47 (dd, 1 H, Jab = 20, JB, H6a, or JB, H7a, ^1.5 Hz), 2.84 (m, 2 H, -CH2Ar), 7.18 (m, 4 H, -CeH4-); mass spectrum (70 eV) m/e (rel intensity) 240 (M+, 72), 224 (79), 205 (31), 195 (49), 180 (58), 165 (38), 150 (39), 130 (49), 120 (69), 90 (100).…”

“…In spite of the notable achievements in the total synthesis of diterpene alkaloids, there are only a limited number of methods so far available for satisfactory realization of this objective. These can be classified only in three narrow groups, namely (1) intramolecular functionalization of C-4 or a C-10 angular methyl group in an appropriately constructed tri-6a-d~f or tetracyclic40-81 system; (2) intramolecular alkylation46-6®-11 at C-4 in a tricyclic system through a functionalized C-10 angular methyl group; and (3) by conjugated addition of hydrocyanic acid. 4a The methods included under 1 and 2 suffer not only from low yields and multiplicity in their reaction paths, but also from the synthetic problems associated with the starting materials containing at least two to three asymmetric centers.…”

Studies on the syntheses of heterocyclic compounds. 675. A facile regiospecific and stereocontrolled synthesis of a diterpene alkaloid intermediate from benzocyclobutenes

“…A crucial step in the synthesis of these types of natural products is the introduction of a functionalized carbon unit at the C-4a angular position in combination with C-l substituents with appropriate stereochemical control in the phenanthrene ring. 5 Hitherto, two general methods have been available; one is an introduction of a suitable group into the C-4a angular position of hydrophenanthrene,6,7 and the other is a direct synthesis from 0-tetralone derivatives having a functionalized group at the a position by Robinson annelation. 7,8 Previously, we have reported a simple total synthesis of the isoquinoline alkaloids9™13 by a regioselective electrocyclic reaction or cycloaddition of the cyanated o-quinodimethane to ¡mines14 and olefins.…”