Recent advances made in synthetic applications of organotin reagents are reviewed with emphasis on (1) Sn-Hbond reactions and resulting cyclizations, (2) Sn-Metal reagents, (3) allylstannanes and carbonyl additions, (4) metal exchange of organotin reagents involving Pd (0) catalysis, and (5) Sn-hetero atom bond reactivities, distannoxane catalyses, and Sn-S bond reactions.
Organotion-compounds coordinated by Lewis bases are far active substrates in comparison with non-coordinated ones. (1) The addition of tributyltin ω-haloalkoxides to heterocumulenes was accelerated in coordinative solvents. (2) The complexes of organotin iodides with phosphine oxides could act as talent catalysts for the cycloaddition of a variety of oxiranes and heterocumulenes, where selective β-cleavage of oxiranes was promoted. (3) Adding HMPA, tributyltin hydride exhibited highly ionic reactivity to reduce only the carbonyl moiety in α-chloro ketones. Catalytic use of tetraphenylstibium iodide allows for novel cycloadditions; (1) cycoladdition of carbon dioxide with oxetanes, (2) cycloaddition of heterocumulenes with monosubstituted oxiranes via selective α-cleavage of oxiranes.
Enantiodifferentiating transformation of a prochiral hydroxyl group of polyols possessing σ-symmetry provides versatile chiral building blocks which can be incorporated into diverse target structures. We have developed nonenzymatic methods which are applicable to a variety of prochiral diols and triols by utilizing l- or d-menthone as chiral template. Thus, 2-substituted 1, 3-propanediols and meso-1, 2-, 1, 3-, and 1, 4-diols are enantiodifferentiatingly functionalized by utilizing a highly stereoselective ring-cleavage reaction of spiroacetal derived from l-menthone. A stereoselective synthesis of meso-1, 3, 5-pentanetriols and their enantioselective transformation by the reaction with l-menthone are also described.
Asymmetric homogeneous hydrogenation of a-acylaminoacrylic acids and analogs, catalyzed by rhodium (I) complexes containing a variety of optically active diphosphines which render the chiral information through the metal center to the substrate, became one of the most successful and well-understood catalytic reactions during these two decades. A case study of the improvement of enantioselectivity in the rhodium (I) -catalyzed hydrogenation of 3-phenyl-3-butenoic acid, a substrate with rather weakly coordinating ability, is discussed. Highly versatile asymmetric catalytic hyderogenation of prochiral acrylic acids with use of new Ru (II) -BI-NAP complexes as catalyst precursors is briefly described. In order to achieve the high level of enantioselective hydrogenation and diastereoselective one as well, a necessary assistance of the proximate functional groups in either prochiral or chiral olefin substrates for making a chelate coordination to the catalyst is exemplified, typically in the hydroxy or carbamoyl group-directed hydrogenation of allylic alcohols and allylic carbamates, respectively.
Three general cyclization methods of macrocycles by carbon-carbon bond formation are presented. In the first method (eq.1), recifeiolide (6), phoracantholide J (7) and 13-, 16-membered lactones 8, 9 were synthesized by the intramolecular alkylation of a carbanion generated from a-haloalkyl phenylthioacetate 1. In the second method (eq.2), zearalenone (15) and lasiodiplodin (16) were synthesized by the intramolecular alkylation of a carbanion generated from α-haloalkyl 2-phenylthiomethylbenzoate 10. In the third method (eq.3, 4, 5), macrocyclic ketones, enones and keto lactones, such as exaltone (17), muscone (18), deoxy-trans-resorcylide (19), deoxy-cis-resorcylide (20), zearalenone (15), germacrone (25), humulene (26), bicyclohumulenone (27), acoragermacrone (28) and mukulol (29), were synthesized by the intramolecular alkylation of a carbanion generated from protected cyanohydrins. Moreover stereoselective syntheses of periplanone B (30), 6 (5β) -an-drostene-3, 17-dion (57), costunolide (76) and haageanolide (77), and discussions of the stereoselectivity of the epoxidation of the enone (35), the transannular Diels-Alder reaction of the (E, E, E) -macrocyclic triene (59) and the [2.3] -Wittig rearrangement of the 13-membered diallylic ether 87 and 96 based on ab-initio MM 2 calculations are presented.
Non-Kekulé molecules are conjugated diradicals (or their homologous poly-radicals) for which no cassical Kekulé structures can not be written. Spectroscopic direct observation of the non-Kekulé molecules, for example, trimethylenemethane and tetramethyleneethane, are surveyed.