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As a result of enormous ring strain, cyclopropene compounds display a range of diverse reactivities in both noncatalytic and transition-metal-catalyzed transformations, thus presenting unique opportunities for organic synthesis. [1,2] To further enhance the synthetic potential of cyclopropenes, the development of expeditious methods for the synthesis of enantioenriched cyclopropenes is highly desirable.[3] In this context, a cyclopropenation reaction of alkynes with diazo compounds that is catalyzed by chiral dirhodium(II) complexes represents one of the most powerful means for the construction of this class of optically active building blocks. Doyle, Müller, and co-workers were the first to demonstrate asymmetric induction (up to ! 98 % ee) in cyclopropenation reactions of terminal alkynes including propargyl alcohol or propargylamine derivatives with diazoacetates using [Rh 2 (5S-mepy) 4 ] (2 a; Scheme 1) as a chiral catalyst.[4] Doyle et al. also reported an enantioselective intramolecular cyclopropenation of diazoacetates, in which [Rh 2 (4S-ibaz) 4 ] (2 b) provided macrocyclic cyclopropenes in up to ! 99 % ee.[5] Corey and coworkers demonstrated that a new mixed carboxylate/carboxamidate catalyst [Rh 2 (OAc)(dpti) 3 ] (3) is highly exceptional for cyclopropenation of a broad range of terminal alkynes with ethyl diazoacetate.[6] The extension of this methodology to include a-substituted a-diazoacetates is particularly attractive because it has the capability to form cyclopropenes with a quaternary stereogenic carbon center. [7][8][9] Although high levels of enantioselectivity (up to 99 % ee) in cyclopropenations of terminal alkynes with aryldiazoacetates [7a] or arylvinyldiazoacetates [7b] under catalysis by [Rh 2 (S-dosp) 4 ] (4) have been reported by Davies and co-workers, the goal for the reaction with a-alkyl-a-diazoesters remains elusive because of the propensity to form a,b-unsaturated esters through a 1,2-hydride shift.[10] Panne and Fox recently disclosed that dirhodium(II) tetrapivalate exhibits high selectivity for cyclopropenation over alkene formation in the reaction of terminal alkynes with a-alkyl-a-diazoesters. [11,12] However, to the best of our knowledge, an enantioselective version of this reaction has not been reported.Our research group has previously demonstrated the first examples of highly enantio-, diastereo-, and chemoselective intramolecular C À H insertion reactions of a-alkyl-a-diazoesters by using dirhodium(II) tetrakis[N-phthaloyl-(S)-tertleucinate] ([Rh 2 (S-pttl) 4 ], 1 a) in which high levels of asymmetric induction (up to 95 % ee) were achieved. [13][14][15] Herein, we report that [Rh 2 (S-tbpttl) 4 ] (1 f), a new dirhodium(II) carboxylate complex that incorporates N-tetrabromophthaloyl-(S)-tert-leucinate as chiral bridging ligands, catalyzes the cyclopropenation reaction of terminal alkynes with 2,4-dimethyl-3-pentyl a-alkyl-a-diazoacetates to give 1,2-disubstituted 2-cyclopropenecarboxylates in good to high yields and with up to 99 % ee. Scheme 1. Chiral dirhodium(II) com...

Regulation of the synthesis of procollagen and other extracellular matrix components was examined in human skin fibroblasts obtained from donors of various ages, from fetal to 80 years old (in vivo aged), and in fetal fibroblasts at varying passage levels (in vitro aged). Growth rates and saturation densities of fibroblasts decreased with increasing age of the donor and after passage 20 of fetal fibroblasts. The rates of collagen and proteoglycan synthesis also decreased during both types of aging to about 10-25% of the rate in early passage fetal fibroblasts, whereas the synthesis of total noncollagenous proteins was not greatly affected. Decreased collagen synthesis in both types of aging was correlated with lower steady-state levels of mRNAs for the two subunits of type I procollagen mRNA, although their regulation was not coordinate. Type III collagen mRNA levels also declined in both types of aging. The concentration of fibronectin mRNA also decreased during in vitro aging but more rapidly than the collagen mRNAs, whereas in fibroblasts from 51-80-year-old donors, it was similar to or higher than in early passage fetal fibroblasts. This study suggests that the decreased synthesis of procollagen and proteoglycans in in vivo aged fibroblasts represents changes that are responsible for intrinsic degenerative changes that occur in human skin during aging. Furthermore, although in vitro and in vivo aging were similar in many respects, they were not equivalent, as evidenced by the differences in regulation of fibronectin expression.

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An assembled insoluble catalyst, PdAS, prepared from palladium ((NH4)2PdCl4 (1)) and non-cross-linked amphiphilic copolymer poly(N-isopropylacrylamide-co-4-diphenylstyrylphosphine) (2) was developed. It was found that PdAS is an excellent catalyst for the Suzuki-Miyaura reaction on three points: (1) The use of 8 x 10(-7) to 5 x 10(-4) mol equiv of PdAS afforded the coupling products efficiently after easy workup, with the turnover number reaching up to 1,250,000. (2) The catalyst was reusable many times without loss of catalytic activity. (3) PdAS showed good stability in any reaction medium (i.e., water or aqueous or anhydrous organic solvents). Analytical study of PdAS indicates that the phosphines in 2 coordinate to palladium to form PdCl2(PPh2Ar)2 species.