A new P‐heterocyclic family: A variety of six‐membered and bridged P‐heterocycles with 1‐benzyl substituent

The ring enlargement of 1‐benzyl‐2,5‐dihydro‐1H‐phosphole oxide ( 1 ) via the corresponding 2‐phosphabicyclo[3.1.0]hexane 2‐oxide ( 2 ) afforded, depending on the conditions, the double bond isomers ( A and B ) of 1,2‐dihydrophosphinine oxide 4 or that of 3‐substituted 1,2,3,6‐tetrahydrophosphinine oxides 5 and 6 . Dihydrophosphinine oxides ( 4 ) were suitable starting materials for 1,2,3,4,5,6‐hexahydrophosphinine oxide 7 and 1,2,3,6‐tetrahydrophosphinine oxide 8 obtained by reductive approaches and for the double bond isomers ( A and B ) of 2‐phosphabicyclo[2.2.2]octadiene 2‐oxide 9 and phosphabicyclooctene oxide 10 prepared in Diels–Alder cycloaddition. Precursor 9 was utilized in the fragmentation‐related phosphorylation of alcohols. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:28–34, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20363     

The synthesis of optically active P‐heterocycles

Optically active 1‐alkoxy‐ and 1‐amino‐3‐phospholene oxides were synthesized by the reaction of the corresponding 1‐chloro‐3‐phospholene oxides with (1R,2S,5R)‐(–)menthol and (S)‐(–)‐α‐phenylethylamine. The 3‐methyl‐3‐phospholene oxides were subjected to dichlorocyclopropanation under liquid–liquid phase transfer catalytic conditions to afford the 3‐phosphabicyclo[3.1.0]hexane 3‐oxides as a mixture of four diastereomers. Thermolysis of the menthyl‐phosphabicyclohexane oxides led to the corresponding 1,2‐dihydrophosphinine oxide as a diastereomeric mixture of two double‐bond isomers. As a result of additional steps, the dichlorocarbene addition reaction of the 1‐menthyl‐3,4‐dimethyl‐3‐phospholene oxide resulted in eventually, the formation of a 4‐dichloromethylene‐1,4‐dihydrophosphinine oxide. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:271–277, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20599     

Fragmentation‐related phosphinylations using 2‐aryl‐2‐phosphabicyclo[2.2.2]oct‐ 5‐ene‐ and ‐octa‐5,7‐diene 2‐oxides

A series of new P‐methylphenyl P‐heterocycles are introduced. The para and ortho substituted 2,5‐dihydro‐1H‐phosphole oxides ( 1a and 1b ) were converted to the double‐bond isomers ( A and B ) of 1,2‐dihydrophosphinine oxides ( 3a and 3b ) via the corresponding phosphabicyclo[3.1.0]hexane oxides ( 2a or 2b ). Isomeric mixture ( A and B ) of the dihydrophosphinine oxides ( 3a and 3b ) gave, in turn, the isomers ( A and B ) of phosphabicyclo[2.2.2]oct‐5‐enes ( 4a and 4b ) or a phosphabicyclo[2.2.2]octa‐5,7‐diene ( 5 ) in Diels‐Alder reaction with dienophiles. The bridged P‐heterocycles ( 4 and 5 ) were useful in the photo‐ or thermoinduced fragmentation‐related phosphinylation of hydroxy compounds and amines. The new precursors ( 4a and 4b ) were applied in mechanistic investigations. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:443–451, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10176     

The synthesis of six‐membered P‐heterocycles with sterically demanding substituent on the phosphorus atom

The ring enlargement of 1‐(2,4,6‐trialkylphenyl)2,5‐dihydro‐1H‐phosphole oxides ( 1 ) via 6,6‐dichloro‐3‐Phosphabicyclo[3.1.0]hexanes ( 2 ) afforded the double‐bond isomers of 1,2‐dihydrophosphinine oxides ( 3 ). Catalytic hydrogenation of the isomeric 1‐(di‐tert‐butyltolyl)‐1,2‐dihydrophosphinine oxides ( 3a ) gave the diastereomers of phosphinane oxide ( 4 ), while that of the 1‐(tri‐isopropylphenyl) isomers ( 5 ) led predominantly to phospholane oxides ( 6 ) formed by ring contraction. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:528–533, 2001     

Microwave‐Promoted Efficient Synthesis of 2‐Phosphabicyclo[2.2.2]octadiene‐ and Octene‐2‐oxides under Solvent‐Free Conditions in Diels–Alder Reaction

The microwave‐induced and solvent‐free Diels–Alder reaction of 1,2‐dihydrophosphinine oxides (1 and 5) and dimethyl acetylenedicarboxylate or N‐phenylmaleimide afforded 2‐phosphabicyclo[2.2.2]octadiene‐ (2 and 6) and phosphabicyclo[2.2.2]octene oxides (4 and 7), respectively, almost quantitatively and in a fast reaction in an ecofriendly manner.     

Preparation,structure, and optical properties of chiral sulfoxides and disulfoxide with a trithiole ring

Optically active 4,9‐diethyl[1,4]‐dithiino[5,6‐f]benzo[1,2,3]trithiole 5‐oxide ( 3 ) and 4,9‐diethyl[1,4]dithiino[5,6‐f]benzo[1,2,3]trithiole 5,8‐dioxide ( 4 ) were obtained by the asymmetric oxidation of 6,11‐diethyl[1,4]dithiino[5,6‐h]benzo[1,2,3,4,5]pentathiepin ( 1 ). The reaction was accompanied by desulfurization and ring‐contraction reactions of the pentathiepin ring. Similarly, optically active 4,8‐diethyl[1,3]dithiolo[4,5‐f]benzo[1,2,3]trithiole 5‐oxide ( 7 ) was produced by the analogous asymmetric oxidation of 6,10‐diethyl[1,3]dithiolo[4,5‐h]benzo[1,2,3,4,5]pentathiepin ( 2 ). The specific rotations of 3 , 4 , and 7 were measured in chloroform, and their optical purity was verified by ¹H NMR with a shift reagent [Eu(hfc)₃]. The structures of 4 and 7 were determined by X‐ray crystallography using Cu Kα radiation, and the absolute configuration of the sulfinyl group was examined based on the Flack parameter, which revealed that 4 has an RR configuration, while 7 has an S configuration. The circular dichroism spectra of 3 , 4 , and 7 were measured in chloroform. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:88–94, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10104     

Cyclobutane-substituted diacetamido sulfides and 2,5-diacylthiophenes

A general and convenient route for the synthesis of 2,5-di[1-methyl-1-arylcyclobutane-3-yl]- thiophenes 4a–c and bis[1-methyl-1-arylcyclobutane-3-yl]-2-(2-oxyethtylamido)thiazole sulfides 7a–c is reported. The characterization of these compounds was obtained by elemental analyses, IR, ¹³C, and ¹H NMR techniques. © 2003 Wiley Periodicals, Inc. 15:26–31, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/.hc10207     

Synthesis of 3‐substituted pyrido[4′,3′:4,5]thieno[2,3‐d]pyrimidines and related fused thiazolo derivatives

Convenient syntheses of 3‐substituted ethyl 4‐oxo‐2‐thioxo‐1,2,3,4,5,6,7,8‐octahydropyrid[4′,3′:4,5]thieno[2,3‐d]pyrimidine‐7‐carboxylates 3a, b, 6, 11–13 , ethyl 3‐methyl‐5‐oxo‐2,3,6,9‐tetrahydro‐5 H‐pyrido[4′,3′:4,5]thieno[2,3‐d][1,3]thiazolo[3,2‐a]pyrimidine‐8‐7H‐carboxylate ( 4 ), and ethyl 2‐methyl‐5‐oxo‐2,3,6,9‐tetrahydro‐5H‐pyrido[4′,3′:4,5]thieno[2, 3‐d][1,3]thiazolo[3,2‐a]pyrimidine‐8[7H]carboxylate ( 8 ) from diethyl 2‐isothiocyanato‐4,5,6,7‐tetrahythieno[2,3‐c]pyridine‐3,6‐dicarboxylate ( 1 ) are reported. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:201–207, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10131     

Studies with condensed amino‐thiophenes: Further investigation of reactivity of amino‐thieno‐coumarines and amino‐thieno‐benzo[h]coumarines toward electron‐poor olefins and acetylenes

The reaction of 3‐amino‐5‐oxa‐2‐thia‐cyclopenta[a]naphthalene‐4‐one 2b with substituted acetylenes afforded C‐1 alkylation products. On the other hand, reaction of 17‐amino‐15‐methyl‐11‐oxa‐16‐thiacyclopenta[a]phenanthrene‐12‐one 5 with substituted acetylenes and electron‐poor olefins afforded the condensed thienopyridine derivatives 7 and 11a – c . The reaction of 5 with acrylonitrile and with 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione afforded compounds 13 and 21 with loss of H₂S via the expected [4 + 2] cycloaddition sequence. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:502–507, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20047     

Preparation of Optically Active Six‐Membered P‐Heterocycles: A 3‐Phosphabicyclo[3.1.0] hexane 3‐oxide,a 1,2‐Dihydrophosphinine 1‐oxide,and a 1,2,3,6‐Tetrahydrophosphinine 1‐oxide

The earlier described a 3‐methyl‐1‐phenyl‐3‐phospholene 1‐oxide ( 1 ) → 6,6‐dichloro‐1‐methyl‐3‐phenyl‐3‐phosphabicyclo[3.1.0]hexane 3‐oxide ( 2 ) → 4‐chloro‐1‐phenyl‐1,2‐dihydrophosphinine 1‐oxide ( 3 ) → 4‐chloro‐5‐methyl‐1‐phenyl‐1,2,3,6‐tetrahydrophosphinine 1‐oxide ( 4 ) reaction sequence was investigated from the point of view of preparing optically active intermediates/products ( 2–4 ). In principle, both the resolution of the corresponding racemic products and the transformation of the optically active starting materials are suitable approaches for the preparation of optically active six‐membered P‐heterocycles ( 2–4 ). Racemization occurred during the dichlorocyclopropanation reaction of (S)‐3‐methyl‐1‐phenyl‐3‐phospholene 1‐oxide ((S)‐ 1 ), but the thermolytic ring opening of (−)‐ 2, and the selective reduction of α,β‐double bond of (−)‐ 3 did not cause the loss of optical activity. First in the literature, the resolution of a 3‐phosphabicyclo[3.1.0]hexane 3‐oxide ( 2 ) and a 1,2,3,6‐tetrahydrophosphinine 1‐oxide ( 4 ) was elaborated. © 2013 Wiley Periodicals, Inc. Heteroatom Chem 24:179–186, 2013; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21080     

Syntheses of new conformationally constrained S‐[2‐[(1‐iminoethyl)amino] ethyl]homocysteine derivatives as potential nitric oxide synthase inhibitors

The efficient syntheses of two new types of conformationally constrained S‐[2‐[(1‐iminoethyl)amino]ethyl]homocysteine derivatives, 1‐amino‐3‐[2[(1‐iminoethyl)amino]ethylthio]cyclobutane carboxylic Acid ( 5 ) and (4S)‐4‐[[2‐[(1‐Iminoethyl)amino]ethyl]thio]‐L‐proline ( 6 ), are reported. These molecules represent the first attempts to probe conformational constraint near the α‐amino acid moiety of known homocysteine‐based inhibitors of nitric oxide synthase. Targets 5 and 6 were evaluated as potential inhibitors of the three human isoforms of nitric oxide synthase. © 2002 John Wiley & Sons, Inc. Heteroatom Chem 13:77–83, 2002; DOI 10.1002/hc.1109     

Synthesis of H‐Phosphinates by the UV Light–Mediated Fragmentation‐Related Phosphorylation Using Simple P‐Heterocycles

Photolysis of aryl‐substituted 2,5‐dihydrophosphole oxides (5a–e and 8) in the presence of methanol afforded methyl aryl‐H‐phosphinates (2a–e) in good yields. In the case of 1‐ethyl‐, cyclohexyl‐, or ethoxy‐2,5‐dihydrophosphole oxides, the reaction was much slower (5f and 5h) or did not take place at all (5g). In such instances, the presence of an additional skeletal methyl group (7) or the use of the more strained 7‐phosphanorbornene derivatives (6) promoted the fragmentation‐related phosphorylations. Furthermore, the effect of the ring saturation in 8 and the possible extensions to 2‐phosphabicyclo[3.1.0]hexanes (10a and 10f), a 1,2‐dihydrophosphinine oxide (11), and a 1,2,3,4,5,6‐hexahydrophosphinine oxide (12) were also investigated. Model compounds with P‐phenyl substituent that are of sufficient ring strain (8, 10a, and 11) could be utilized well.     

N-[4-(dicyanomethylazo)phenyl]-2-saccharin-2-ylacetamide in the synthesis of pyridazine and pyrimidine derivatives

N-[4-(Dicyanomethylazo)phenyl]-2-saccharin-2-ylacetamide ( 2 ) proved to be a convenient precursor for the synthesis of a variety of pyridazine and pyrimidine derivatives 4a,b,6 , and 7 . Also a series of substituted pyrimidines 10–16 were prepared from the reaction of N-[4-(2-amino-1-cyano-2-substitutedvinylazo)phenyl]-2-(saccharin-2-yl)acetamide 9a,b with different reagents via initial addition to either the cyano or amino group, followed by cyclization. Some of the synthesized heterocycles were screened for their biological activity. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 15:2–8, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10194     

Crystal structures and molecular modeling of 1,8 chalcogenide‐substituted naphthalenes

The molecular structures of naphtho[1,8‐cd][1,2]dithiole, naphtho[1,8‐cd][1,2]diselenole, naphtho[1,8‐cd][1,2]ditellurole, naphtho[1,8‐cd]‐ [1,2]dithiole 1‐oxide, naphtho[1,8‐cd][1,2]dithiole 1,1‐dioxide, and naphtho[1,8‐cd][1,2]dithiole 1,1,2‐trioxideand naphtho[1,8‐cd][1,2]dithiole 1,1,2,2‐tetroxide are compared. The E–E distance varies, broadly reflecting the degree of distortion imposed by the rigid naphthalene backbone as well as the degree of oxidation at sulfur. Index Entry: The naphthalene backbone imposes shortening of E–E bond lengths when E = S and Se compared to Ph E E Ph systems but is itself subject to distortion as a consequence of the steric bulk of the E atoms. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:530–542, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20055     

2‐Ethyl‐2‐phosphabicyclo[2.2.2]oct‐7‐ene derivatives: Synthesis and use in fragmentation‐related phosphorylations

A 2‐phosphabicyclo[2.2.2]oct‐7‐ene oxide ( 2 ) and a 2‐phosphabicyclo[2.2.2]octa‐5,7‐diene oxide ( 3 ) with ethyl substituent on the phosphorus atom was synthesized and their fragmentation properties were studied. The phosphabicyclooctadiene oxide ( 3 ) could be utilized in both the UV light‐mediated phosphorylation of simple alcohols and in the thermoinduced phosphorylation of hydroquinone giving an easy access to P‐ethylphosphinates (e.g., 4 and 6 ). The phosphabicyclooctene oxide ( 2 ) was, however, not useful in photoinduced phosphorylations; under such conditions the precursor ( 2 ) underwent dechlorination to afford 5 . © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:196–199, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20093     

Thiophenylhydrazonoacetates in heterocyclic synthesis

Benzo[b]thiophen-2-yl-hydrazonoesters 4 were synthesized by coupling of 2-diazo-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxamide ( 1 ) with either ethyl cyanoacetate or ethyl acetoacetate. The reactivity of 4 toward a variety of nitrogen nucleophiles was investigated to yield pyrazole, isoxazole, pyrimidine, triazine, pyrazolopyridine, and pyrazolopyrimidine derivatives. © 2003 Wiley Periodicals, Inc. 15:15–20, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/.hc10205     

New 7‐membered diazepanone alkoxyamines for nitroxide‐mediated radical polymerization

The synthesis of new 7‐membered diazepanone alkoxyamines [2,2,7,7‐tetramethyl‐1‐(1‐phenyl‐ethoxy)‐[1,4]diazepan‐5‐one ( 3 ) and 2,7‐diethyl‐2,3,7‐trimethyl‐1‐(1‐phenyl‐ethoxy)‐[1,4]diazepan‐5‐one ( 8 )] through the Beckmann rearrangement of piperidin‐4‐one alkoxyamines was developed. Both 3 and 8 were evaluated as initiators and regulators for the nitroxide‐mediated radical polymerization of styrene and n‐butyl acrylate. 8 , a sterically highly hindered alkoxyamine readily available as a crystalline solid, allowed the fast and controlled polymerization and preparation of polymers with low polydispersity indices (1.2–1.4) up to a degree of polymerization of about 100. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3332–3341, 2004     

Oligomeric calix[4]arene‐thiacrown ether for toxic heavy metals

A new oligomeric calix[4]arene‐thiacrown‐4 ( 5 ) was synthesized via a condensation reaction of 5,11,17,23‐tetra‐tert‐butyl‐25,27‐bis‐(4‐aminobenzyloxy)‐calix[4]arene‐thiacrown‐4 ( 4 ) with adipoyl dichloride. In this oligomerization reaction only five/six calix[4]arene‐thiacrown‐4 units were linked in the oligomeric chain. The complexation studies of 5 were made with liquid–liquid‐ extraction and solid–liquid‐sorption procedures. For comparison, the extraction efficiencies of monomers 1 , 3 , and 4 to selected transition metals are reported. The selectivity of monomers 3 and 4 toward Cu²⁺, Hg²⁺, and Pb²⁺ was lost after oligomerization in the two‐phase extraction systems. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 186–193, 2004     

3/4‐phenylene bisheterocycles from ring transformation reaction of sydnone derivatives: Synthesis of 3‐[3/4‐heterocyclyl]phenyl‐5‐methyl‐3H‐[1,3,4]‐oxadiazol‐2‐ones from 3/4‐acetylphenylsydnones and their biological properties

The bifunctional 3/4‐[acetyl]phenylsydnones 1a, 1b were subjected to a one‐pot ring conversion to 3‐[3/4‐acetyl]phenyl‐5‐methyl‐3H‐[1,3,4]‐oxadiazol‐2‐ones 2a, 2b , which on further bromination yielded the 3‐[3/4‐bromoacyl]phenyl‐5‐methyl‐3H‐[1,3,4]‐oxadiazol‐2‐ones 3a, 3b . Reaction of these compounds with thiourea yielded the 3‐[3/4‐(2‐aminothiazol‐4‐yl)]phenyl‐5‐methyl‐3H‐[1,3,4]‐oxadiazol‐2‐ones 4a, 4b . The other thiazole derivatives 5a, 5b–7a, 7b were prepared by using thiosemicarbazide, thioacetamide, and thiobenzamide, respectively. In another reaction of the bromoacetyl compounds ( 3a, 3b ) with 2‐aminopyridine and 2‐aminothiazole, the fused biheterocyclic compounds 3‐[3/4‐imidazo‐[1,2‐a]pyridine‐2‐yl]phenyl‐5‐methyl‐3H‐[1,3,4]‐oxadiazol‐2‐ones 8a, 8b and 3‐[3/4‐imidazo‐[2,1‐b]‐thiazol‐6‐yl]phenyl‐5‐methyl‐3H‐[1,3,4]‐oxadiazol‐2‐ones 9a, 9b were obtained. The 3‐[3/4‐(benzofuran‐2‐carbonyl)]phenyl‐5‐methyl‐3H‐[1,3,4]‐oxadiazol‐2‐ones 10a, 10b were obtained by treatment of compounds 3a, 3b with o‐hydroxy benzaldehyde. Most of these compounds exhibited antifungal activity greater than the reference drugs used. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:50–54, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20255     

Cationic and mesoionic 1,3‐thiazolo‐[3,2‐c]quinazoline derivatives

4‐Allylthio‐2‐arylquinazolines 4a–c undergo cyclization by action of bromine to furnish 5‐aryl‐3‐bromomethyl‐2,3‐dihydrothiazolo[3,2‐c]quinazolin‐4‐ium bromides 5a–c . Compounds 5a–c undergo ring opening by action of water under acid catalysis to afford the corresponding dibromide derivatives 6a–c . Bromination of 3‐allyl‐2‐aryl‐4(3H)quinazolinethiones 7a–c leads to 5‐aryl‐2‐bromomethyl‐2,3‐dihydrothiazolo[3,2‐c]quinazolin‐4‐ium bromides 8a–c . However, anhydro‐3‐hydroxy‐5‐aryl‐1,3‐thiazolo[3,2‐c]quinazolin‐4‐ium hydroxide 10a–c were prepared by the cyclodehydration of the corresponding thioglycolic acids 9a–c with Ac₂O. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:576–580, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10148