Abstract:Dedicated to Joe P. Richmond on the occasion of his 60 th birthday.Abstract: Enantiomerically pure 2-iodocyclopropylboronic esters 6 and 8 have been synthesized from the readily available allylic alcohol 2 via an oxidation-radical decarboxylation sequence. These unique building blocks have been demonstrated to be versatile intermediates for a consecutive Suzuki-coupling with aryl-, heteroaryl-, alkenyl-, and cyclopropylboron derivatives (1 example each).
“…A bulky chiral auxiliary at boron efficiently suppressed homocoupling of trans - 739 , allowing for selective cross-coupling between the cyclopropyl iodide and external boronic acid to give the corresponding products 740 in good yields. Remarkably, cis - 739 reacted readily as well, providing the corresponding cyclopropylboronic ester 741 (Scheme ) . The obtained boronic esters 740 and 741 can further be utilized as nucleophilic components in the second Suzuki−Miyaura cross-coupling reaction or in other stereoselective transformations of cyclopropyl boronates, such as oxidation into cyclopropanols or Matteson homologation. ,, 243 …”
“…A bulky chiral auxiliary at boron efficiently suppressed homocoupling of trans - 739 , allowing for selective cross-coupling between the cyclopropyl iodide and external boronic acid to give the corresponding products 740 in good yields. Remarkably, cis - 739 reacted readily as well, providing the corresponding cyclopropylboronic ester 741 (Scheme ) . The obtained boronic esters 740 and 741 can further be utilized as nucleophilic components in the second Suzuki−Miyaura cross-coupling reaction or in other stereoselective transformations of cyclopropyl boronates, such as oxidation into cyclopropanols or Matteson homologation. ,, 243 …”
“…[44] Following this report, the Suzuki-Miyaura coupling between cyclopropyl iodides and cyclopropyl boronates was used to elaborate contiguous cycloA C H T U N G T R E N N U N G propane arrays, [45] whereas 2-iodocyclopropylboronates were identified as useful building blocks for the preparation of 1,2-disubstituted cyclopropanes. [46] Additionally, industrial researchers reported the use of a Negishi coupling between ethyl cis-2-iodocyclopropanecarboxylate and an arylzinc A C H T U N G T R E N N U N G reagent as a key step in the process development of the non-nucleoside reverse transcriptase inhibitor MIV-150. [47] To further expand the scope of palladium-catalyzed reactions involving functionalized iodocyclopropanes, we investigated the feasibility of Sonogashira cross-couplings.…”
The copper-free Sonogashira coupling between N-substituted cis- 2-iodocyclopropanecarboxamides and terminal aryl-, heteroaryl-alkynes or enynes, followed by 5-exo-dig cyclization of the nitrogen amide onto the carbon-carbon triple bond, provides a remarkably efficient access to a variety of substituted 4-methylene-3-azabicyclo[3.1.0]hexan-2-ones in excellent yields. Protonation of these latter enamides generates bicyclic N-acyliminium ions that can be involved in Pictet-Spengler cyclizations leading to new 3-azabicyclo[3.1.0]hexan-2-ones, possessing a quaternary stereocenter at C4, with high diastereoselectivities. This strategy constitutes an attractive complementary alternative to the classical route that relies on the addition of organometallic reagents to cyclopropyl imides.
“… Additionally, prefunctionalization of the acid with an alkyl chloroformate and CDI proved to be useful . Other successful esterification techniques include the use of pyrithione derivatives, such as 305 , ,− 306 , and disulfide dipyrithione 307 (in combination with tributylphosphine) . The purity of reagent 305 was found to have a profound effect on the reaction yield …”
Section: Pioneering and Classical Methodsmentioning
Decarboxylative halogenation, or
halodecarboxylation, represents
one of the fundamental key methods for the synthesis of ubiquitous
organic halides. The method is based on conversion of carboxylic acids
to the corresponding organic halides via selective cleavage of a carbon–carbon
bond between the skeleton of the molecule and the carboxylic group
and the liberation of carbon dioxide. In this review, we discuss and
analyze major approaches for the conversion of alkanoic, alkenoic,
acetylenic, and (hetero)aromatic acids to the corresponding alkyl,
alkenyl, alkynyl, and (hetero)aryl halides. These methods include
the preparation of families of valuable organic iodides, bromides,
chlorides, and fluorides. The historic and modern methods for halodecarboxylation
reactions are broadly discussed, including analysis of their advantages
and drawbacks. We critically address the features, reaction selectivity,
substrate scopes, and limitations of the approaches. In the available
cases, mechanistic details of the reactions are presented, and the
generality and uniqueness of the different mechanistic pathways are
highlighted. The challenges, opportunities, and future directions
in the field of decarboxylative halogenation are provided.
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