445. Photochemical transformations. Part XVII. Improved methods for the decarboxylation of acids

Abstract

The photochemical decarboxylation of acyl hypoiodites has been investigated and shown to provide an efficient method for the preparation of the corresponding nor-iodides. Primary and secondary carboxylic acids are readily decarboxylated by using the lead tetra-acetate-iodine reagent. The recently discovered t-butyl hypoiodite has been shown to form acyl hypoiodites at room temperature. With this reagent primary, secondary, and tertiary acids, as well as the hitherto intractable glutaric and adipic acids, can be decarboxylated without difficulty.Some aspects of our work have already been reported in preliminary form.1 THE Hunsdiecker method for the decarboxylation of acids is well It suffers from certain disadvantages amongst which the difficulty and expense of preparing dry silver salts may be mentioned. Recently Cristol et aL3 introduced a modified Hunsdiecker procedure, using mercuric salts, which has certain advantages. At the initiation of our own worktye argued that if acyl hypoiodites could be prepared conveniently they might well be induced to decompose photochemically at relatively low temperatures into iodide and carbon dioxide. The important discovery of Wettstein and his collaborators that the hypoiodites from alcohols can be prepared advantageously by the in situ interaction of lead tetraacetate, alcohol, and iodine suggested that acyl hypoiodites might be obtained similarly.6 Our experiments soon provided evidence that this was correct and that in many cases decarboxylation proceeded smoothly on illumination with a tungsten lamp. All the * Part XVI, J., 1964, 2518.

Synthetic Studies on Cyathin Terpenoids: Enantioselective Synthesis of the Tricyclic Core of Cyathin through Intramolecular Heck Cyclisation

“…We therefore decided to convert the propionate side chain into an iodoethyl appendage before activating the carbonyl group. Thus saponification of 35a followed by the Kochi reaction [Pb(OAc) 4 /I 2 , CCl 4 at reflux] [20] produced the iodo ketone 39 in 65 % overall yield. Unfortunately, attempts to introduce the required enol triflate on this sensitive material using Tf 2 O met with failure.…”

“…To this end, iodide (R)-13 was synthesised as a model system because it could be easily prepared from the readily available keto ester (R)-10 (ee = 91 %). [17a] Thus, saponification of 10 followed by iododecarboxylation of acid 12 according to the Barton modification of the Kochi reaction [20] gave rise to iodo ketone 13 in 81 % overall yield. After the protection of the carbonyl of 13 as a trimethylsilyl enol ether using TMSOTf, the iodide 14 was condensed with cyclohepta-2,4,6-trienecarbonitrile 8a [21] using LDA as a base.…”

Synthesis of a Cn–Cn+6 Building Block Common to Important Polyol,Polyene Antibiotics from a Divinylcarbinol by a Desymmetrizing Sharpless Epoxidation

“…This suggests that this HO 2 C–CH 2 O– group was decarboxylated oxidatively and the resulting carboxonium ion CH 2 =O + – scavenged by an acetate ion from one of the heavy metal salts 59. The degradation of HO 2 C–CH 2 O– to AcO–CH 2 O– in the bis(carboxylic acid) 37 proceeded smoothly and went to completion within 20 min only when the reaction mixture was irradiated 60. In the absence of light the substrate failed to react during as much as 4 h (at room temp.)…”

In situ formed tert-butyl hypoiodite as an efficient oxidant for rapid, room temperature, metal-free aromatization of Biginelli 3,4-dihydropyrimidin-2(1H)-ones under basic conditions

“…38 For example, Barton used this species to prepare N-iodoamides 39 and to decarboxylate carboxylic acids. 40 Other authors have used it in the preparation of esters from carboxylic acids and alkyl iodides, 41 and in the iodination of aromatics with strong electron donor substituents. The usual literature method for the preparation of tert-butyl hypoiodite is the reaction of tert-butyl hypochlorite with either molecular iodine or metal iodides, or by the reaction of potassium tert-butoxide with molecular iodine.…”