Gordon L. Lange

Facile Conversion of Primary and Secondary Alcohols to Alkyl Iodides

Abstract A convenient, simple procedure is described for the conversion of a variety of primary and secondary alcohols to iodides in yields ranging from 60–98%. The method employs the Ph3P/imidazole/I2 combination of reagents in the solvent dichloromethane.

Structural elucidation and synthesis of new components isolated from Piper sarmentosum (Piperaceae)

Abstract Six components were Isolated from the fruit of Piper sarmentosum . Two of the components are the ubiquitous β-sitosterol and the known unsaturated amide, pellitorine, 3. The other four components, which are new natural products, consist of the aromatic alkene 1, the pyrrole amide 2 and two unsaturated pyrrolidine amides which have been given the names sarmentine 4 and sarmentosine 5 . Components 1 and 2 were synthesized to establish unambiguously their structures.

Synthesis of the spirosesquiterpene (−)-acorenone and related cyclopentanoid monoterpenes

The first total synthesis of the spirosesquiterpene (−)-acorenone (1) is described. The critical step involves a spiroannelation of the enamine of aldehyde 11 with 1-methoxy-3-buten-2-one (16) in t...

Asymmetric induction in mixed [2 + 2] photoadditions. Effect of solvent, alkene concentration and temperature

Abstract In mixed [2 + 2] photoadditions with the chiral auxiliary in either the enone or the alkene component, it was found that changing the polarity of the solvent or the temperature of the irradiation had a marked effect on the extent of asymmetric induction.

Asymmetric induction in simple [2 + 2] photoadditions

Photochemical cycloaddition of cyclopentene with enone esters 1 containing different chiral auxiliaries yielded anti and syn adducts 2 and 3 in good yield and with moderate to high (79%) enantiomeric excesses.

SYNTHESIS OF THE GUAIANE ()-ALISMOL USING A FREE RADICAL FRAGMENTATION/ELIMINATION SEQUENCE

The first synthesis of the guaiane alismol (3) is reported. The efficient, stereoselective and regioselective approach involves only eight steps, with the key transformation being a radical fragmentation/elimination sequence which proceeds in high yield (92%).

Asymmetric induction in mixed photoadditions: Employing α,β-unsaturated homochiral ketals

Abstract Diastereomeric excesses as high as 84% were achieved in [2 + 2] photoadditions of methyl 3-oxo-1-cyclohexene-1-carboxylate with α,β-unsaturated homochiral ketals prepared from 2-cyclopentenone and 2R,3R-tartrate esters.

Synthesis of the sesquiterpenoid trichodiene using a free radical fragmentation approach

Abstract A highly regio- and stereoselective synthesis of the sesquiterpenoid trichodiene is reported. The approach requires only nine steps starting with a [2+2] photoaddition and employs the free radical fragmentation of an “external” cyclobutane bond in a key step.

An N-methyl aristolactam and an oxygenated cyclohexane derivative from Piper ribesioides☆

Abstract Investigation of the fruit and stems of Piper ribesioides afforded eight known compounds in addition to the first natural N -methylaristolactam and a complex cyclohexenediol, known previously only as a synthetic product.

Reversal of regioselectivity with increasing ring size of alkene component in [2+2] photoadditions

Abstract Photoaddition of cyclohexenones 1a or 1b to methyl cyclobutene- ( 2 ), cyclopentene- ( 5 ) or cyclohexenecarboxylate ( 9 ) shows a gradual reversal of regioselectivity from head-to-head ( 3a/b ) to head-to-tail adducts ( 11a/b ). These results are inconsistent with the generally accepted dipolar interaction model.