The 1,3-dipolar cycloaddition of chiral 1-alkyl-1,2-diphosphacyclopenta-2,4-dienes ((1-(−)-menthyl)oxymethyl-1,2-diphosphole and 1-(+)-neomenthyl-1,2-diphosphole) with diphenyldiazomethane leads to novel P-chiral bicyclic phosphiranes having six chiral centers. The degree of diastereoselectivity depends on the substituent at phosphorus, and dramatically increases in the case of (+)-neomenthyl group (de up to 71%). DFT calculations indicate that the cycloaddition is thermodynamically controlled.