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Iterative Synthesis of Semicorrins, Tripyrrolines, and Higher Analogs J. Am. Chem. Soc. 1999, 121, 1958.

Sonogashira coupling of I and 2,2-dimethyl-4-pentynamide followed by 5-exo-dig cyclization gave 71% of the tripyrroline II with E,Z-geometry that was confirmed by x-ray anal. Repetition of this sequence of activation, coupling, and cyclization afforded the secocorphin deriv. III in 60% yield. The E,E,Z-geometry of III was derived from the hydrogen bonding between rings C and D and steric repulsion between rings A-C.

Studies on Corrin Synthesis. A Solution to the Introduction of Meso Substituents J. Org. Chem. 1999, 64, 1778.

The authors describe the oxidative addn. of MeC.tplbond.CCH2C(Me)2CO2H to 2-chloro-3,3,5-trimethyl-1-pyrroline-5-carbonitrile followed by ammonolysis and reductive elimination to give meso substituted semicorrin (I).

Synthesis of 1,2,3,7,8,9-Hexahydrodipyrrins and Secocorrins:Important Precursors for the Construction of Corrins Org. Lett. 1999, 1, 341.

Hexahydrodipyrrins (I) (R = H, Me; R1, R2, R3, R4 = H2 or Me2; X = H2) have been prepd. by two routes: Pd(0)-initiated coupling/cyclization of triflates (II)and alkyne amines RC.tplbond.CCR3CR4CH2NH2 and redn. of semicorrins I (X = O).

Total Synthesis of (.+-.)-Stemoamide J. Am. Chem. Chem. 1997, 119, 3409.

(.+-.)-Stemoamide (I) was prepd. in seven steps beginning with .gamma.-chlorobutyryl chloride and succinimide, which were efficiently converted to the key acetylenic oxazole II on a 20 g scale. Intramol. (Diels-Alder)-(retro-Diels-Alder) reaction of II, with in situ hydrolysis of methoxyfuran III, then gave butenolide IV, in a novel reaction that may involve the initial formation of the radical cation of II. The remaining two stereocenters in I were established in a single step by a highly selective redn. of IV (NaBH4/NiCl2), followed by equilibration to the thermodynamically favored natural configuration.

Studies on the Synthesis of Phytochrome and Related Tetrapyrroles. Dihydropyrromethenones by Photochemical Rearrangement of N-Pyrrolo Enamides J. Org. Chem. 1997, 62, 2894.

Dihydropyrromethenone I, a potential precursor for the synthesis of phytochrome, has been prepd. in enantiomerically pure form beginning with N-aminopyrrole II and (2R,3R,3'S)-HC.tplbond.CCH(CMe2OH)CHMeCO2H. The key step involved a 3,5-sigmatropic rearrangement of N-pyrrolo enamide III. Related compds. were similarly prepared.

Dihydropyrromethenones by Pd(0)-Mediated Coupling of Iodopyrroles and Acetylenic Amides. Synthesis of the A,B-Ring Segment of Phytochrome J. Org. Chem. 1997, 62, 2907.

Dihydropyrromethenone deriv. I, which constitutes the A,B-ring segment of phytochrome, has been prepd. in enantiomerically pure form beginning with (2R,3R,1'S)-HC.tplbond.CCH(CHMeOH)CHMeCONHCH2C6H4OMe-4 and the iodopyrrolepropanoate. The key steps involved the TBAF-catalyzed 5-exo-dig cyclization of the acetylenic pyrrole II, followed by thia-Mitsunobu inversion of the resulting alc. deriv.

Enantioselective synthesis of beta-amino acids using the Nicholas reaction Enantiosel. Synth. .beta.-Amino Acids 1997, 359.

A review with 10 refs. on use of the Nicholas reaction to prep. homochiral acetylenic acids for the enantioselective synthesis of .beta.-amino acids.

Enantioselective syntheses of (+)- and (-)-blastmycinolactol Tetrahedron. Lett. 1997, 38, 6621.

(-)-Blastmycinolactol (I, R = H) was prepd. in an enantioselective fashion from acetylenic acid II via a three step sequence involving debenzylation-lactonization, hydration with concurrent C3-epimerization, and Baeyer-Villiger oxidn. accompanied by ester cleavage. Acylation of I (R = H) with isovaleryl chloride then afforded (+)-blastmycinone (I, R = Me2CHCH2CO) in excellent overall yield.

Formal Total Syntheses of the .beta.-Lactam Antibiotics Thienamycin and PS-5 J. Org. Chem. 1996, 61, 2413.

Chiral nonracemic acetylenic acids of general structure I, prepd. using the Schreiber modification of the Nicholas reaction, have been converted to .beta.-amino acid derivs. of type II by a two-step sequence involving Curtius rearrangement followed by oxidative cleavage of the acetylenic bond. Amino acid derivs. II are excellent precursors for .beta.-lactams of the carbapenem class, including the important antibiotics thienamycin (III) and PS-5 (IV).

Toward the Synthesis of Biologically Important Chlorins, Isobacteriochlorins, and Corrins. Cyclic Enamides from Acetylenic Amides J. Org. Chem. 1996, 61, 5013.

Cyclic enamides I of a type useful in the synthesis of naturally occurring chlorins, isobacteriochlorins, and corrins have been prepd. by a process involving 5-exo-dig cyclization of the appropriate acetylenic amides II. The desired cyclization is catalyzed by either n-Bu4NF or LiAl(NHBn)4.

An improved synthesis of the C,D-ring pyrromethenone of phytochrome and phytochromobilin Tetrahedron Lett. 1996, 37, 6069.

Pyrromethenone (I), the C,D-ring segment of both phytochrome and phytochromobilin has been prepd. in a highly efficient fashion by conversion of 2-acetylbutyrolactone to the Z-enol triflate followed by Pdo catalyzed coupling with trimethylsilylacetylene, p-chlorophenylselenide ring opening, and amidation, to afford ring-D synthon II having the proper geometry and oxidn. state for conversion to I.

Enantioselective syntheses of (+)- and (-)-phaseolinic acid Tetrahedron Lett. 1996, 37, 8297.

(+)- And (-)-Phaseolinic acid have been prepd. in an enantioselective fashion from (2S,3S,4R)-HO2CCHMeCH(C.tplbond.CH)CH(OCH2Ph)(CH2)4Me (I) by a three-step sequence involving lactonization, epimerization at C-3, and oxidative cleavage. I was obtained as a single enantiomer using a Nicholas-Schreiber reaction.

Enynones in Organic Synthesis. 8. Synthesis of the Antimicrobial-Cytotoxic Agent Juncusol and Members of the Effusol Class of Phenols J. Org. Chem. 1995, 60, 376.

Two new syntheses of phenols have been developed which have been utilized in an efficient prepn. of the antimicrobial-cytotoxic agent juncusol and several members of the effusol class of phenols. These results complement earlier studies with enynones (RCH2)2C:CHCOC.tplbond.CMe [I, R = H, Ph] and provide for the highly efficient conversion of I to either methylenecyclopentenones or phenols with virtually 100% selectivity.

Synthesis of cyclic enamides by intramolecular cyclization of acetylenic amides Tetrahedron Lett. 1995, 36, 1193.

Cyclic enamides, e.g. I, of a type useful in the synthesis of naturally occurring chlorins, isobacteriochlorins, and corrins have been prepd. by a process involving Nicholas-Schreiber condensation to afford acetylenic amides, followed by either n-Bu4NF- or LiAl(NHBn)4-catalyzed ring closure.

An unequivocal synthesis of the ring-A,B dihydropyrromethenone of phytochrome Tetrahedron Lett. 1995, 36, 1197.

Dihydropyrromethenone I, a potential precursor for the synthesis of phytochrome, has been prepd. in enantiomerically pure form beginning with the homochiral acetylenic lactone II.

A conceptually new approach to the synthesis of linear tetrapyrroles related to phytochrome Tetrahedron Lett. 1995, 36, 2717.

Linear tetrapyrroles, e.g. I, of a type related to phytochrome, have been prepd. by TBAF catalyzed 5-exo-dig cyclization of bisacetylenic amides, e.g. II.

Enynones in Organic Synthesis. 6. Synthesis of Spirocyclic Methylenecyclopentenones and Analogs of the Methylenomycin Class of Antibiotics. Mechanism of Phenol Catalysis J. Org. Chem. 1994, 59, 5292.

Spirocyclic methylenecyclopentenones of general structure I (R = Me, Ph, H, R1 = H, Me, n = 1, 2) were prepd. in a single step from bis-acetylenic alcs. II by a process involving initial oxy-Cope rearrangement to afford (Z)-enynones III followed by electrocyclic ring closure. Mechanistic studies indicate that the initial step leading from III to I is a thermal 1,5-prototropic shift to afford dienols which can cyclize by a symmetry-allowed (.pi.4s + .sigma.2s + .pi.2a) process. This last step is catalyzed by certain phenols having low oxidn. potentials, most likely by a mechanism involving single electron transfer. Dramatic rate enhancements were also obsd. for the cyclization of simple enynones RC.tplbond.CCOCH:CACHBC (A = CH2Ph, Me, Et, Bu, CHMe2, B = Ph, H, Me, Et, Pr, C = H, Me, R2 = Me, H) to methylenecyclopentenones IV upon catalysis with either .alpha.-tocopherol (vitamin E) or tert-butylcatechol. Further enhancements in both rate and yield were obtained under conditions of photoassisted single electron transfer (PET), which afforded IV in yields of 80-98%.

Enynones in Organic Synthesis. 7. Substituent Effects on the .alpha.-Tocopherol-Catalyzed Cyclization of Enynones to Methylenecyclopentenones. Convenient Syntheses of Members of the Methylenomycin Class of Antibiotics J. Org. Chem. 1994, 59, 5305.

Substituent effects on the .alpha.-tocopherol (vitamin E) catalyzed cyclization of a wide variety of enynones RC.tplbond.CCOCD:CACHB (I, A = Me, EtO, EtOCH2, H, CHMe2, B = H, Et, EtO CH2OSiMe2CMe3, CH2OTHP, THP = 2-tetrahydropyranyl, D = H, Me, Ph. 4-MeOC6H4, SPh, etc., R = H, Me, Ph, CO2Et, SiMe3, etc.) to methylenecyclopentenones II have been examd., with particular emphasis given to electron-withdrawing and -donating groups at positions 2-4 and 6. In general, electron-withdrawing groups at positions 4 and 6 dramatically accelerate the cyclization process, while strong electron-donating groups at positions 3 and 4 completely inhibit reaction. Relatively little effect is exerted by groups at C-2, except for the Et ester deriv. I (A = R = Me, B = H, D = CO2Et), which is totally unreactive. This methodol. was employed in the syntheses of the methylenecyclopentenone antibiotics methylenomycin B II (A = D = Me, B = R = H) and desepoxy-4,5-didehydromethylenomycin A III and in formal syntheses of methylenomycin A and xanthocidin.

A perspective on the contributions to heterocyclic chemistry by Professor Edward C. Taylor of Princeton University Heterocycles. 1993, 35, 1.

The many contributions in heterocyclic chem. are described of professor Edward C. Taylor, esp. rearrangements in synthesis.

versatile synthesis of .beta.-amino acids using the Nicholas reaction. II. Formal total synthesis of thienamycin Tetrahedron Lett. 1993, 34, 2585.

Homochiral acetylenic acid I, prepd. using the Schreiber modification of the Nicholas reaction, was converted to .beta.-amino acid II by a two step sequence involving Curtius rearrangement followed by oxidative cleavage of the acetylenic bond. II was then converted to thienamycin precursor III by cyclization with DCC followed by epimerization.

A versatile synthesis of .beta.-amino acids using the Nicholas reaction. I. Application to .beta.-lactams of the carbapenem class Tetrahedron Lett. 1993, 34, 2581.

Homochiral acetylenic acids I (R = H, Me, PhCH2O), prepd. using the Schreiber modification of the Nicholas reaction, were coverted to .beta.-amino acids II by a two step sequence involving Curtius rearrangement followed by oxidative cleavage of the acetylenic bond. II are excellent precursors for .beta.-lactams of the carbapenem class.

A convenient synthesis of pyrrole- and N-aminopyrrole-3-propionate esters Heterocycles. 1993, 35, 1103.

Trisubstituted pyrroles I (R = Et, PhCH2, R1 = H; R = Et, R1 = phthalimido, NH2) having a substitution pattern found in many naturally occurring linear and macrocyclic tetrapyrroles have been prepd. in a regiospecific fashion by a two step sequence involving Diels-Alder reaction of CH2:CHCOCO2R (R = Et, PhCH2) with CH2C(OR1)CH:CHMe (R1 = Et, TMS, TBDMS, TIPS) followed by ozonolysis and Paal-Knorr cyclization.

A convenient synthesis of methylenomycin B. Further mechanistic studies on the SET catalyzed electrocyclization of enynones Tetrahedron Lett. 1992, 33, 2265.

Methylenomycin B (I) was prepd. in .apprx.55% yield by SET catalyzed cyclization of enynone Me2C:CMeCOC.tplbond.CH. Mechanistic studies indicate that initial electron donation takes place at C-3 in enolized intermediates of type CH2:CMeCMe:C(OH)C.tplbond.CH.

Bis-heteroannulation. 16. A synthetic approach to geigerin J. Org. Chem. 1992, 57, 6305.

Furano alc. I (R = H, R1 = OH), the key intermediate in the proposed synthesis of the guaianolide sesquiterpene geigerin (II), was prepd. by a novel sequence of reactions which includes a chemoselective oxy-Cope transformation of enynols of general structure III (R2 = H). Although III itself underwent oxy-Cope reaction with exclusive triple-bond participation, the corresponding tert-butyldimethylsilyl ether III (R2 = SiMe2CMe3) gave the desired vinyl silyloxy Cope product IV with 100% selectivity. The conversion of acetylenic oxazole IV to I (R = H, R1 = OH) was then effected by a highly efficient Diels-Alder-retro-Diels-Alder transformation to generate the guaiane ketone I (RR1 = O), followed by hydride redn.

Bis-heteroannulation: total synthesis of furanoterpenes, butenolides, lactones and related materials Adv. Heterocycl. Nat. Prod. Synth. 1992, 2, 251.

A review with 47 refs. on the bis-heteroannulation approach to the synthesis of furanoterpenes, butenolides, .gamma.-lactones, and related compds.

Tetrapyrroles. III. Homochiral dihydropyrromethenones from N-aminopyrroles and acetylenic acids Tetrahedron Lett. 1992, 33, 6231.

Dihydropyrromethenone I, a potential precursor for the synthesis of Phytochrome, Phycocyanin, and Phycoerythrin, was prepd. in homochiral form from pyrrolohydrazide II by a sequence involving F- induced 5-exo-dig cyclization to afford enamide III, followed by photochem. 3,5-sigmatropic rearrangement.

Tetrapyrroles. V. Formal syntheses of the ring-C,D pyrromethenones of phytochrome and phycocyanin Tetrahedron Lett. 1992, 33, 6239.

Formal syntheses of pyrromethenones I (R = Et, CH:CH2), potential intermediates for the prepn. of phycocyanin and phytochrome resp., was accomplished by Pd0 mediated coupling of iodopyrrole II with acetylenic amides III (R = H, SeC6H4Cl-4) followed by F-catalyzed 5-exo-dig cyclization and DDQ oxidn.

Tetrapyrroles. IV. A highly efficient synthesis of homochiral dihydropyrromethenones via palladium(0) mediated coupling of iodopyrroles and acetylenic amides Tetrahedron Lett. 1992, 33, 6235.

Homochiral dihydropyrromethenones I [R = H, PhCH2; R1 = H, Me; R2 = H, Me, (S)-CHMeOMe] were prepd. in a highly efficient manner by Pd0 mediated coupling of iodopyrrole II with acetylenic amides III, followed by F- catalyzed 5-exo-dig cyclization. In analogous fashion, phytochrome precursor IV was prepd. in 85% overall yield.

A novel synthesis of juncusol Tetrahedron Lett. 1991, 32, 1279.

Juncusol (I) has been prepd. beginning with the known .beta.-tetralone deriv. II via novel electrocyclization of the alkynone III.

2-Oxo-3-butenoate esters as dienophiles and their utility in a novel synthesis of pyrroles Tetrahedron Lett. 1991, 32, 1765.

Trisubstituted pyrroles, e.g., I (R = Et, CH2Ph) were prepd. in a regiospecific fashion by a two step sequence involving Diels-Alder reaction of 2-oxo-3-butenoate esters R1CH:CHCOCO2R (R = Et, Ch2Ph, R1 = H, Ph) with 2-alkoxy-1,3-pentadienes MeCH:CHCH(OR2):CH2 [R2 = Et, SiMe3, SiMe2CMe3, Si(CHMe2)3], followed by ozonolysis and Paal-Knorr cyclization.

Bis-heteroannulation. 15. Enantiospecific syntheses of (+)- and (-)-norsecurinine J. Am. Chem. Soc. 1991, 113, 5384.

(-)-Norsecurinine (I) was prepd. in a stereospecific fashion with the acetylenic oxazole II as the starting material. Diels-Alder cyclization of II afforded the furano ketone III, which was transformed in five steps to the butenolide mesylate IV (R = MeSO2). Transannular alkylation of IV (R = MeSO2) then afforded I. In identical fashion, ent-II gave (+)-norsecurinine. The structure of ent-IV (R = H) was detd. by x-ray anal.

Total synthesis of (.+-.)-gnididione and (.+-.)-isognididione J. Org. Chem. 1990, 55, 202.

(.+-.)-Gnididione I (.beta.-Me) and (.+-.)-isognididione I (.alpha.-Me), furanosesquiterpenes from Gnidia latifolia, were totally synthesized from oxazole aldehyde II via the intermediate alcs. (3Z)-R- and (3E)-R-III.