K. C. Kumara Swamy

Mitsunobu and Related Reactions: Advances and Applications

10. Patented Literature 2616 10.1. Esterification 2616 10.2. Ether Formation 2619 10.2.1. Etherification without Cyclization 2619 10.2.2. Etherification with Cyclization 2624 10.3. N-Alkylation 2625 10.4. Other Reactions 2627 11. Summary and Outlook 2628 12. Note Added in Proof 2628 13. Abbreviations Used in This Review 2629 14. Acknowledgments 2629 15. Supporting Information Available 2630 16. References 2630

Ruthenium-Catalyzed Synthesis of Isoquinolones with 8-Aminoquinoline as a Bidentate Directing Group in C–H Functionalization

Ruthenium-catalyzed oxidative annulation of N-quinolin-8-yl-benzamides with alkynes in open air has been achieved using 8-aminoquinolinyl moiety as a bidentate directing group in the presence of Cu(OAc)2·H2O as an oxidant. This reaction offers a broad substrate scope, and both symmetrical and unsymmetrical alkynes can be applied. High regioselectivity was achieved in the case of unsymmetrical (aryl)alkynes. Reaction with heteroaryl amides was also successful in this catalytic process. A ruthenium-N-quinolin-8-yl-benzamide complex was isolated in the absence of alkyne; in the absence of both N-quinolin-8-yl-benzamide and alkyne, in contrast to literature, only the monoacetate complex RuCl(OAc)(p-cymene), but not the bis-acetate complex Ru(OAc)2(p-cymene), was isolated. These data suggest that this reaction may proceed via N,N-bidentate chelate complex. Key products were characterized by X-ray crystallography.

Palladium-catalyzed annulation of allenes with indole-2-carboxylic acid derivatives: synthesis of indolo[2,3-c]pyrane-1-ones via Ar-I reactivity or C-H functionalization.

Two methodologies, one involving Ar-I reactivity and the other through C-H functionalization, for the formation of indolo[2,3-c]pyrane-1-ones via the corresponding allenes, are presented. A highly efficient approach to indolo[2,3-c]pyrane-1-one derivatives through the Pd-catalyzed regioselective annulation of allenes with 3-iodo-1-alkylindole-2-carboxylic acids is described. This method is fairly general for a wide range of allenes affording the respective indolo[2,3-c]pyrane-1-ones in good to excellent yields. In addition, a Pd(II)-catalyzed oxidative coupling of indole-2-caboxylic acid derivatives with allenes via direct C-H functionalization to afford the corresponding indolo[2,3-c]pyrane-1-ones in moderate to good yields has been developed.

Allenylphosphonates/Allenylphosphine Oxides as Intermediates/Precursors for Intramolecular Cyclization Leading to Phosphorus-Based Indenes, Indenones, Benzofurans, and Isochromenes

Utilizing internally available functional groups, a simple protocol for the efficient synthesis of phosphorus-based indenes, indenones, benzofurans, and isochromenes via intramolecular cyclization of allene intermediates/precursors is generated; the latter intermediates/precursors are conveniently obtained through aldehyde-, alkylidene-, and hydroxyl-functionalized propargyl alcohols and P(III)-Cl precursors. The structures of key products have been unequivocally confirmed by X-ray crystallography.

Reactivity of allenylphosphonates toward salicylaldehydes and activated phenols: facile synthesis of chromenes and substituted butadienes.

The reaction of salicylaldehydes with allenylphosphonates in the presence of a base leads to a variety of phosphono-chromenes and allylic phosphonates. Optimization of reaction conditions reveals that DBU (base) in DMSO (solvent) is the best combination in most cases, with DBU acting as an organocatalyst. PEG-400 also gave good results, but the yields were slightly lower than that in DMSO. Several of the key products have been characterized by single-crystal X-ray crystallography. Interconversion of E and Z isomers of phosphono-chromenes is demonstrated by (31)P NMR spectroscopy. A novel P-C bond cleavage reaction of some of these chromenes leading to substituted enones is also reported. In a few cases, phenol addition products are also isolated. In order to probe the pathways in the latter reaction, allenylphosphonates have also been treated with activated phenols in the presence of base to selectively afford either allylic phosphonyl ethers or vinylic phosphonyl ethers depending on the substituents on the allenylphosphonate. Theoretical calculations were consistent with experimental results. Finally, utilization of allylic phosphonyl ether in the Horner-Wadsworth-Emmons reaction to afford substituted trans-1,3-butadiene in good yields is demonstrated.

Use of Elemental Sulfur or Selenium in a Novel One-Pot Copper-Catalyzed Tandem Cyclization of Functionalized Ynamides Leading to Benzosultams.

A novel and efficient [Cu]-catalyzed one-pot regio- and stereospecific synthesis of benzo[1,4,2]dithiazine 1,1-dioxides and benzo[1,4,2]thiaselenazine 1,1-dioxides by cyclization of functionalized ynamides with elemental sulfur/selenium has been developed. Its generality is elegantly illustrated by extension to benzodithiazepines and benzothiaselenazepines. Involvement of water in the reaction is demonstrated by the incorporation of (2)D at the olefinic site by using D2O in place of water. Selective oxidation at sulfur in benzo[1,4,2]dithiazine 1,1-dioxide by using mCPBA as the oxidizing agent is also described.

Divergence in the reactivity between amine- and phosphine-catalyzed cycloaddition reactions of allenoates with enynals: one-pot gold-catalyzed synthesis of trisubstituted benzofurans from the [3 + 2] cycloadduct via 1,2-alkyl migration and dehydrogenation.

Regioselective synthesis of functionalized dihydropyran derivatives by DABCO-catalyzed [2 + 4] cycloaddition of allenoates with enynals or enynones has been developed. Phosphine-catalyzed [3 + 2] cycloaddition of allenoates with enynals provides 1,1-alkyne (aldehyde)-substituted cyclopentenes wherein enynals act as electrophiles. These alkyne-tethered cyclopentenes upon [Au]/[Ag] catalysis lead to substituted benzofurans via 1,2-alkyl migration and dehydrogenation (aromatization). One-pot reaction of allenoates with enynals using sequential phosphine and gold catalysis is also reported. The cyclopentene obtained from the PPh3-catalyzed reaction of allenoate H2C═C═CH(COO-t-Bu) with enynal undergoes decarboxylation under the [Au]/[Ag] catalysis and forms a carboxylate-free benzofuran. The structures of key products are confirmed by single-crystal X-ray analysis.

Synthesis and structures of new bicyclic 1,3-Di-t-butyl-1,3,2-λ3, 4-λ3-diazadiphosphetidines containing ten- and eleven-membered rings

Abstract The reaction of [t-BuNPCl]2 (1a) with the diols 2,2′-dimethyl-1,3-propanediol, 2,2′-methylenebis(6-t-butyl-4-methylphenol), bis(2-hydroxy-1-naphthyl)methane and 2,2′-biphenyldimethanol affords the novel bicyclic compounds [(t-BuN)P]2[-OCH2CMe2CH2O-] (2),{[(t-BuN)P]2[O-6-t-Bu-4-Me-C6H2]2CH2} (3), {[(t-BuN)P]2[2-O-1-C10H6]2CH2} (4) and {[(t-BuN)P]2[2-OCH2-C6H4]2} (5). The structures of 3.1/2C6H6 and 4 in the solid state have been determined by X-ray crystallography. Analogous reaction of 1a with 2,2′-biphenol affords three products, one of which is [2,2′-(C6H4O)2P]2(2,2′-OC6H4)2 (6); this compound is formed by cleavage of the cyclodiphosphazane ring.

Cycloaddition Reactions of Allenylphosphonates and Related Allenes with Dialkyl Acetylenedicarboxylates, 1,3-Diphenylisobenzofuran, and Anthracene

Cycloaddition reactions of allenylphosphonates [(RO)(2)P(O)[(R(1))C═C═CR(2)(2)] with dialkyl acetylenedicarboxylates, 1,3-diphenylisobenzofuran, and anthracene have been investigated and compared with those of allenoates [(EtO(2)C)RC═C═CH(2)] and allenylphosphine oxides [Ph(2)P(O)(R(1))C═C═CR(2)(2)] in selected cases. Allenylphosphonates (RO)(2)P(O)(Ar)C═C═CH(2) with an α-aryl group preferentially undergo [4 + 2] cycloaddition with DMAD/DEAD under thermal activation, but in addition to the expected 1:1 (allene: DMAD) product, the reaction also leads to 1:2 as well as 2:1 products that were not reported before. When an extra vinyl group is present at the γ-carbon of allenylphosphonate [e.g., (OCH(2)CMe(2)CH(2)O)P(O)(Ph)C═C═CH(C═CHMe)], [4 + 2] cycloaddition takes place utilizing either the vinylic or the aryl end, but additionally a novel cyclization wherein complete opening of the [β,γ] carbon-carbon double bond of the allene is realized. In contrast to these, the reaction of allenylphosphonate (OCH(2)CMe(2)CH(2)O)P(O)(H)C═C═CMe(2) possessing a terminal ═CMe(2) group with DMAD occurs by both [2 + 2] cycloaddition and ene reaction. While the reaction of ═CH(2) terminal allenylphosphonates as well as allenylphosphine oxides with 1,3-diphenylisobenzofuran afforded preferentially endo-[4 + 2] cycloaddition products via [α,β] attack, the analogous allenoates [(EtO(2)C)RC═C═CH(2)] underwent exo-[4 + 2] cyclization. Under similar conditions, allenylphosphonates with a terminal ═CR(2) group gave only [β,γ]-cycloaddition products. An unusual ring-opening of a [4 + 2] cycloaddition product followed by ring-closing via [4 + 4] cycloaddition, as revealed by (31)P NMR spectroscopy, is reported. Anthracene reacted in a manner similar to 1,3-diphenylisobenzofuran, albeit with lower reactivity. Key products, including a set of exo- and endo- [4 + 2] cycloaddition products, have been characterized by single crystal X-ray crystallography.

Vinyl azides derived from allenes: thermolysis leading to multisubstituted 1,4-pyrazines and Mn(III)-catalyzed photochemical reaction leading to pyrroles.

Thermolysis of phosphorus-based vinyl azides under solvent- and catalyst-free conditions furnished a new route for 1,4-pyrazines. A simple one-pot, Mn(III)-catalyzed photochemical route has been developed for multisubstituted pyrroles starting from allenes and 1,3-dicarbonyls via in situ-generated vinyl azides. The utility of new phosphorus-based pyrroles is also demonstrated in the Horner reaction. The structures of key products are unequivocally confirmed by X-ray crystallography.